Question Answer
The specimen is thinly sliced and is placed on the centre of the slide, with the coverslip placed on top e.g. looking at
What is dry mount in the preparation of slides? hair.
Specimen is suspended in liquid on slide and the cover slip is placed at an angle to prevent air bubbles e.g. looking
What is wet mount in sample preparation? at bodily fluid (saliva).
What is smear slides in sample preparation? The edge of a slide is used to smear the sample, creating a thin, even coating on another slide e.g. to observe blood.
Wet mount is prepared first then the coverslip is pressed down to squash the sample e.g. observing mitosis in root
What is squash slide in sample preparation? tips.
Most cells do not absorb much light so there is little contrast, therefore staining creates contrast as different
components within cells take up stains to different degrees, making the different components of the cell more
What does staining do to the slide? visible.
What are the 3 main stains used in preparing a
microscope slide? Iodine, methyl blue (stains nuclei blue/purple), eosin (stains cytoplasm pink)
What is differential staining? More then one stain is used to identify different cellular components and cell types.
It consists of sheets of membranes forming flattened sacs called cisternae. It has ribosomes bound to its surface
What is the role of the rough endoplasmic and it is where translation takes place for secretory proteins, aswell as proteins for the cell membrane and
reticulum? lysosomes.
It consists of sheets of flattened sacs called cisternae and it modifies the polypeptide further and then packages it
into vesicles to be secreted from the cell, form part of the structure of the cell membrane or enter vesicles which
What is the function of the golgi apparatus? can form lysosomes.
What does the final destination of the protein
depend on? The amino acid sequence of the protein and how the protein was modified in the rough ER and golgi apparatus.
What type of cells will have a lot of rough ER? Cells that secrete a lot of proteins.
What is the function of smooth endoplasmic Responsible for synthesis and storage of lipids and carbohydrates. These can then pass through the golgi apparatus
reticulum? and modified before being transported to their final destination.
Why is diffusion enough for single celled The metabolic activity of single celled organisms is low so dont need much energy. Also have a large surface area to
organisms? volume ratio.
What are the features of an effective exchange Increased surface area (provides area needed and overcomes limitations of SA:V ratio), thin layers (short diffusion
surface? distance), surrounded by capillaries (maintains concentration gradient), ventilation
Why do large, multicellular organisms
(mammals) need specialised exchange High metabolic activity increases need for oxygen and diffusion happens too slow. Cells in the centre cannot get
surfaces and transport systems? enough oxygen purely through diffusion as distance is too great.
What is the average size of an alveolus? 100-300 micrometers across
Squamous epithelium provide a short diffusion distance, surfactant prevents surfaces sticking and collapsing of
What are the features of the mammalian lung alveoli due to surface tension of water when air pressure is low, large surface area, ventilation, surrounded by
that enable efficient gas exchange? capillaries
What is required for air to be forced into and
out of the alveoli? A pressure change
What is the diaphragm? A thin sheet of muscle that seperates the thorax (chest) from the abdomen.
What are the two types of intercostal muscles? Internal and external
What happens to the external intercostal
muscles during inspiration? They contract which pulls the rib cage up and out, decreasing the air pressure in the thorax and forcing air in.
What happens to the internal intercostal
muscles during inspiration? They relax
What happens to the internal intercostal
muscles during strong expiration? They contract, bringing the rib cage down and in, increasing the air pressure in the thorax and forcing air out.
What happens to the external intercostal
muscles during expiration? They relax.
What happens to the diaphragm during
inspiration? It contracts, moves down and flattens, decreasing the air pressure as there is a larger volume, forcing air in.
What happens to the diaphragm during
expiration? It relaxes and moves back to its domed shape, increasing the air pressure as the volume is smaller, forcing air out.
It controls the metabolic activities of the cell as it directs the synthesis of all proteins, as it contains coded genetic
What is the function of the nucleus? information.
It is contained within a double membrane called the nuclear envelope which protects the nucleus from damage in
the cytoplasm. The nuclear envelope contains nuclear pores which allow molecules to enter and leave the nucleus
What is the structure of the nucleus and how it e.g. mRNA during protein synthesis. The outer layer of the nucleus envelope is continuous with the rough
is important? endoplasmic reticulum.
They are the sites of the final stages of cellular/aerobic respiration, where the energy stored in the bonds of complex
What is the function of the mitochondria? organic molecules is transferred into the energy carrying molecule called ATP.
It has a double membrane structure, with the outer mitochondrial membrane and the inner mitochondrial
membrane, with the intermembrane space in between. Inside the mitochondria is a fluid called the matrix -
What is the structure of the mitochondria and contains the enzymes needed for the Krebs Cycle. The enzymes for oxidative phosphorylation are found on the
why is it important? inner mitochondrial membrane.
What is the folded structure of the inner
mitochondrial membrane called? Cristae
,Question Answer
What is the importance of cristae on the inner
mitochondrial membrane? There is a great deal of surface area for the enzymes needed for oxidative phosphorylation.
Why does the mitochondria contain a loop of It contains the genes required for some of the enzymes involved in aerobic respiration. Mitochondria also contain
mitochondrial DNA? mitochondrial ribosomes which synthesise the proteins encoded by the mitochondrial DNA.
What type of cells contain a larger number of
mitochondria? Cells that require a large amount of energy e.g. muscle cells.
What is the structure of lysosomes? Specialised forms of vesicles that contain hydrolytic enzymes. They also have an internal acidic fluid.
Why do lysosomes have an acidic internal
fluid? As the lysosomal enzymes have an optimum pH which is acidic.
Digest pathogens in phagocytosis, can be used to destroy organelles that are no longer functional, can transfer
What are the functions of lysosomes? enzymes outside of cell by exocytosis
What does chromatin consist of? DNA coiled around proteins called histones.
What does nucleoplasm contain and what is It is a gelatinous substance inside the nucleus that contains molecules such as nucleotides and enzymes which are
its role? needed for DNA and RNA synthesis.
What does chromatin coil to form and when
are these structures visible? It coils to form chromosomes which only become visible when cells are preparing to divide.
Where ribosomal RNA is produced, which goes on to form part of the structure of ribosomes. The nucleolus is also
What is the function of the nucleolus? where ribosome subunits are assembled.
Vesicles are membranous sacs that have storage and transport roles. They consist of a single membrane with fluid
What is the structure and function of vesicles? inside.
Two layers of phospholipid molecules which contain a non-polar, hydrophobic region which is the two fatty acids,
and it contains a polar, hydrophillic region which is the phosphate group. Due to the hydrophobic nature of the fatty
What is the phospholipid bilayer composed of? acids, the hydrophillic phosphate group is on the exterior and interacts with the environment.
Partially permeable barriers between the cell and its environment, sites of some chemical reactions and also
What are the functions of cell membranes? involved in cell signalling through the diffusion of chemicals.
Why can hydrophobic molecules easily pass
through a phospholipid bilayer? Because the centre of the plasma membrane is hydrophobic and non-polar.
'Fluid' because phospholipid molecules can move around within each layer meaning the membrane is flexible and
Why is the structure of the plasma membrane can change shape. 'Mosaic' because the plasma membrane is studded with protein molecules and the size and
called the 'fluid mosaic model'? arrangement of these proteins varies, much like a mosaic pattern.
What other susbtances does the plasma
membrane contain? Proteins and cholesterol.
One end of the molecule is polar and hydrophillic, which attracts the polar head groups on the phospholipid
What is the structure of cholesterol in relation molecules. The rest of the molecule is non polar and hydrophobic meaning it attracts the non polar, hydrophobic
to hydrophobic and hydrophillic regions? fatty acids in the phospholipid molecules.
Why does the inclusion of cholesterol in the It increases the strength of it as it interacts with the phospholipids, making it more stable and less likely to be
plasma membrane do to it? damaged.
Reduces sideways movements of phospholipids and other molecules within the membrane. This means it controls
What does cholesterol help reduce in the the fluidity of the membrane, preventing it from becoming too fluid under warm conditions and too rigid under cool
plasma membrane? conditions.
Because the cholesterol packs the spaces
between the phospholipids, what does this
reduce? It reduces the movement of water soluble chemicals across the cell-surface membrane.
What are the three cytoskeletal fibres? (widest) Microtubules, intermediate fibres, microfilaments (narrowest)
What are microfilaments made of and what is They are narrow fibres containing the protein actin which can contract. They are involved in cell movement and also
their role? cell contraction during cytokinesis.
What are intermediate fibres made of and what
is their role? They are formed from a number of different proteins and their role is to strengthen the cell.
They are formed from subunits of the protein tubulin, and these subunits assemble to form tubulin polymers, then
What are microtubules made from? forming hollow microtubules.
They are involved in the movement of organelles, they form the spindle fibres that are involved in the movement of
chromosomes during mitosis and meiosis. Lastly, by forming a complex network in the cytoplasm, they help to
What are the functions of microtubules? determine the shape of a cell.
They are composed of a small and large subunit and are constructed of ribosomal RNA made in the nucleolus. They
What is the structure and function of are the sites of protein synthesis as they read the base sequence on the mRNA molecule and use this to order the
ribosomes? amino acids into the correct sequence.
Important in maintaining turgor in the cell so that the contents of the cell push against the cell wall. They do this as
they have a low water potential meaning water enters creating a hydrostatic pressure acting outwards, making the
What is the function of vacuoles? cell turgid.
It is a membrane lined sac in the cytoplasm. The membrane lining is called the tonoplast, and it is selectively
What is the structure of the vacuole? permeable meaning it controls which molecules enter and leave the vacuole.
What are vacuoles if they appear in animal
cells? They are small and transient (not permanent).
Where are chloroplasts not located? Roots
What is the membrane of chloroplasts like? It is a double membrane and it controls which molecules enter and leave the chloroplast.
Membrane bound flattened discs inside the chloroplast that stack to form grana. This is where the light dependent
What are thylakoids? reactions take place.
,Question Answer
Where the light dependent reactions of photosynthesis take place as they contain chlorophyll and enzymes
What is the role of thylakoids? needed.
What is several thylakoids stacked on top of
each other called? Granum
What is the benefit of stacking thylakoids into
grana? Allows light to be absorbed more efficiently.
What are thylakoids on different grana Flattened membranes called lamellae which play a role in light independent reactions and allow chemicals to be
connected by? passed between grana.
A fluid material inside chloroplasts and it is where the light independent reactions take place as it contains the
What is stroma and what is its role? enzymes needed.
What can the glucose produced by
photosynthesis be stored as in chloroplasts? Starch granules
What do chloroplasts contain that allows them They contain a loop of DNA which contains genes which encode for some of the proteins needed for
to synthesise proteins? photosynthesis. They also contain ribosomes which synthesise the proteins encoded by the DNA.
What is the cell wall made of? The polysaccharide cellulose
It is present in every plant cell and it provides strength to the plant cell as it needs to be mechanically strong enough
to resist the hydrostatic force of pressure water inflow. The contents of the cell also press against the cell wall,
making it turgid. It also acts as a defence mechanism, protecting the contents of the cell from invading
What is the function of the cell wall? pathogens.
What can cellulose molecules do to increase They form hydrogen bonds with each other to form larger structures called microfibrils. These form a mesh like
strength of cell wall? structure in the plant cell wall which is extremely strong.
What is the layer of material in between plant The middle lamella which contains polysaccharides as well as calcium and magnesium ions and this acts as a glue
cells called and what is its role? between plant cells.
Where are centrioles not found? Flowering plants and not found in most fungi
What are centrioles made of? Microtubules
What are a pair of centrioles called? Centrosome
They play a role in the assembly of the spindle fibres during mitosis and meiosis - however not essential for spindle
What are the functions of centrioles? assembly. Formation of cilia and flagella.
What is the structure of cilia and flagella? There are 9 pairs of microtubules with another pair in the centre (9+2 structure).
Using energy from ATP, the microtubule pairs can move relative to the pairs next to them, creating the bending
How can cilia and flagella move? motion of these organelles.
They are hairlike organelles that extend from the surface of certain cells. They beat in a ryhtmic manner to waft
matter (e.g. waft mucus in the trachea to the mouth to be swallowed). Stationary cilia play a role in sensing the
What are cilia and what are their functions? chemicals around the cell.
They are whiplike organelles that protrude from the surfaces of certain cells (e.g. sperm cells). Its role is to move the
What are flagella and what are their functions? cell.
What can the cell walls in algae contain? Cellulose and glycoproteins
What are the cell walls of fungi made of? Polysaccharide chitin as well as other polysaccharides and glycoproteins.
How wide is the diameter of a typical ribosome
in a human cell? Around 25 nanometres
What do early and modern light microscopes
have in common? They both have eyepiece lenses, stages and focusing dials.
What was the magnification of the first light
microscopes? Around 300 times
What can a modern light microscope magnify
to? Around 1000 times
What are the advantages of light microscopes We can use light microscopes to view living cells meaning we can explore processes such as cell division and
over other types of microscopes? movement of cells.
What is the problem with light microscopes? The problem of resolution due to the nature of light itself.
The minimum distance between two objects where they can still be seen as two seperate objects. The ability to
What is resolution? distinguish two objects as seperate entities.
What is the limit of resolution on standard light
microscopes? Around 200nm
What is the wavelength of visible light and how
does this affect the resolving power of light
microscopes? The wavelength of visible light is around 400nm to 700nm meaning it reduces the resolving power.
A laser scanning confocal microscope moves a laser across a specimen (point illumination), causing fluorescence
from structures labelled with a dye. The emitted light from the specimen is filtered through a pinhole aperture. The
What happens in laser scanning confocal beamsplitter is a dichroic mirror which reflects one wavelength of light (laser) but allows other wavelengths through
microscopy? (reflected light).
What are the advantages of laser scanning Higher resolution images than conventional light microscopy, can produce 3D images of cells, can visualise
confocal microscopy? specific proteins and structures within cells and watch them move. Non-invasive
Equation for magnification? Image size / actual size
Why is the resolution of electron microscopes
much better than light microscopes? Because electrons have a very short wavelength
, Question Answer
What is the maximum resolving power of
electron microscopes? 0.1nm
The interior of an electron microscope is a vacuum meaning we cannot view living samples. It also requires very
What are the disadvantages of electron careful staining and the specimen often has to be very thin. Can get artefacts (false images created by the staining
microscopes? process or the conditions inside the electron microscope). Expensive
The electron gun provides an electron beam. The inside of an electron microscope is a vacuum so the electrons can
pass through without bouncing of molecules in the air. We can focus the electron beam using electromagnetic
How do transmission electron microscopes lenses. The electron beam then passes through the specimen, producing flat 2D images and only works if specimen
work? is thinly sliced.
What are the advantages and disadvantages of
a TEM? + High resolution - Only works if specimen is thinly sliced, doesnt work on living organisms.
How does a scanning electron microscope In this microscope the electron beam doesn't pass through the specimen but rather scattered from the surface of
work? the specimen and detected.
What are the advantages and disadvantages of + can produce 3D images, specimen does not have to be thinly sliced - lower resolution than a TEM, specimen has
an SEM? to be coated with a metal, leading to potential artefacts.
What is the resolving power of an SEM? 3-10nm
The DNA is contained within a membrane bound nucleus. DNA is tightly wrapped around proteins called histones
which form chromosomes (means they can pack lots of DNA into tight space). Their DNA is a linear molecule
What are the features of eukaryotic cells? (doesnt form loop). Prescence of membrane bound organelles.
What are the ribosomes in eukaryotic cells? 80S
Where is extra chromosomal DNA found in
eukaryotic cells? Certain organelles such as chloroplasts and mitochondria.
How do eukaryotic cells reproduce compared Eukaryotic cells reproduce from asexual or sexual reproduction whereas prokaryotic cells reproduce through binary
to prokaryotic cells? fission.
Which are bigger: Eukaryotes or Prokaryotes? Eukaryotes
What are some key features of prokaryotic No membrane bound organelles at all - DNA is found in cytoplasm rather than nucleus. DNA is arranged into
cells? circular chromosome with no free ends - DNA not bound to histones.
Where is the extra chromsomal DNA found in
prokayotic cells? In small loops of DNA called plasmids.
What is the size of the ribosomes in
prokaryotic cells? 70S
What is the cell wall in bacteria made from? Peptidoglycan - polymer formed between peptides and polysaccharide molecules.
What is the role of the slime capsule on the
outside of the cell wall of bacterium? Can help protect the bacteria from phagocytosis by white blood cells.
They are fine protein strands on the surface of some bacteria and they help bacteria to attach to surfaces and also
What are pilli and what is their function? to other bacteria.
Why are lipid droplets and glycogen granules
important for bacteria? They act as nutrient stores for the bacterial cell.
Infoldings of the cell membrane of prokaryotic cells, however it is believed they are artefacts created when bacterial
What are mesosomes? cells are prepared for electron microscopy.
It is that mitochondria, chloroplasts and possibly other eukaryotic organelles were formally free living prokaryotes
(bacteria). The theory is that these prokaryotes were taken inside another cell as an endosymbiont - an organism
that lives within the body or cells of another organisms. This evenutally led to the evolution of eukaryotic
What is the theory of endosymbiosis? cells.
What is a stage micrometer? A microscope slide with a very accurate scale in micrometres engraved on it.
A glass disc marked with a fine scale of 1-100. The scale has no units and remains unchanged regardless of which
What is an eyepiece graticule? objective lens is being used.
The nucleus contains the genes for the protein needed in the form of DNA. The nucleus is the site of transcription,
where the base sequence of the gene for the protein is copied onto mRNA. mRNA leaves the nucleus through
nuclear pores. The ribosomes are then the sites of translation, these can be on the rough endoplasmic reticulum or
free. The base sequence of the mRNA allows the ribosome to assemble the chain of amino acids. The proteins are
then transported to the golgi apparatus in vesicles (enter cis fase, leave trans face) which are then modified and
Explain how organelles are interlinked for the repackaged into vesicles. These vesicles then fuse with the plasma membrane, with the contents of the vesicle
process of protein synthesis. being secreted by exocytosis.
What equipment is used to measure the
capacity of the lungs? Spirometer
What is meant by tidal volume? The volume of air that is inspired and expired with each resting breath.
The volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest
What is vital capacity? possible intake of breath.
What is inspiratory reserve volume? The maximum volume of air that you can breathe in over a normal inhalation.
The extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe
What is expiratory reserve volume? out.
What is residual volume? The volume of air that is left in your lungs when you have exhaled as hard as possible.
What is the role of ciliated epithelium? They contain cilia which beat back and forth to move the mucus (e.g. back to the mouth to be swallowed).
What is the role of goblet cells? They secrete mucus
The specimen is thinly sliced and is placed on the centre of the slide, with the coverslip placed on top e.g. looking at
What is dry mount in the preparation of slides? hair.
Specimen is suspended in liquid on slide and the cover slip is placed at an angle to prevent air bubbles e.g. looking
What is wet mount in sample preparation? at bodily fluid (saliva).
What is smear slides in sample preparation? The edge of a slide is used to smear the sample, creating a thin, even coating on another slide e.g. to observe blood.
Wet mount is prepared first then the coverslip is pressed down to squash the sample e.g. observing mitosis in root
What is squash slide in sample preparation? tips.
Most cells do not absorb much light so there is little contrast, therefore staining creates contrast as different
components within cells take up stains to different degrees, making the different components of the cell more
What does staining do to the slide? visible.
What are the 3 main stains used in preparing a
microscope slide? Iodine, methyl blue (stains nuclei blue/purple), eosin (stains cytoplasm pink)
What is differential staining? More then one stain is used to identify different cellular components and cell types.
It consists of sheets of membranes forming flattened sacs called cisternae. It has ribosomes bound to its surface
What is the role of the rough endoplasmic and it is where translation takes place for secretory proteins, aswell as proteins for the cell membrane and
reticulum? lysosomes.
It consists of sheets of flattened sacs called cisternae and it modifies the polypeptide further and then packages it
into vesicles to be secreted from the cell, form part of the structure of the cell membrane or enter vesicles which
What is the function of the golgi apparatus? can form lysosomes.
What does the final destination of the protein
depend on? The amino acid sequence of the protein and how the protein was modified in the rough ER and golgi apparatus.
What type of cells will have a lot of rough ER? Cells that secrete a lot of proteins.
What is the function of smooth endoplasmic Responsible for synthesis and storage of lipids and carbohydrates. These can then pass through the golgi apparatus
reticulum? and modified before being transported to their final destination.
Why is diffusion enough for single celled The metabolic activity of single celled organisms is low so dont need much energy. Also have a large surface area to
organisms? volume ratio.
What are the features of an effective exchange Increased surface area (provides area needed and overcomes limitations of SA:V ratio), thin layers (short diffusion
surface? distance), surrounded by capillaries (maintains concentration gradient), ventilation
Why do large, multicellular organisms
(mammals) need specialised exchange High metabolic activity increases need for oxygen and diffusion happens too slow. Cells in the centre cannot get
surfaces and transport systems? enough oxygen purely through diffusion as distance is too great.
What is the average size of an alveolus? 100-300 micrometers across
Squamous epithelium provide a short diffusion distance, surfactant prevents surfaces sticking and collapsing of
What are the features of the mammalian lung alveoli due to surface tension of water when air pressure is low, large surface area, ventilation, surrounded by
that enable efficient gas exchange? capillaries
What is required for air to be forced into and
out of the alveoli? A pressure change
What is the diaphragm? A thin sheet of muscle that seperates the thorax (chest) from the abdomen.
What are the two types of intercostal muscles? Internal and external
What happens to the external intercostal
muscles during inspiration? They contract which pulls the rib cage up and out, decreasing the air pressure in the thorax and forcing air in.
What happens to the internal intercostal
muscles during inspiration? They relax
What happens to the internal intercostal
muscles during strong expiration? They contract, bringing the rib cage down and in, increasing the air pressure in the thorax and forcing air out.
What happens to the external intercostal
muscles during expiration? They relax.
What happens to the diaphragm during
inspiration? It contracts, moves down and flattens, decreasing the air pressure as there is a larger volume, forcing air in.
What happens to the diaphragm during
expiration? It relaxes and moves back to its domed shape, increasing the air pressure as the volume is smaller, forcing air out.
It controls the metabolic activities of the cell as it directs the synthesis of all proteins, as it contains coded genetic
What is the function of the nucleus? information.
It is contained within a double membrane called the nuclear envelope which protects the nucleus from damage in
the cytoplasm. The nuclear envelope contains nuclear pores which allow molecules to enter and leave the nucleus
What is the structure of the nucleus and how it e.g. mRNA during protein synthesis. The outer layer of the nucleus envelope is continuous with the rough
is important? endoplasmic reticulum.
They are the sites of the final stages of cellular/aerobic respiration, where the energy stored in the bonds of complex
What is the function of the mitochondria? organic molecules is transferred into the energy carrying molecule called ATP.
It has a double membrane structure, with the outer mitochondrial membrane and the inner mitochondrial
membrane, with the intermembrane space in between. Inside the mitochondria is a fluid called the matrix -
What is the structure of the mitochondria and contains the enzymes needed for the Krebs Cycle. The enzymes for oxidative phosphorylation are found on the
why is it important? inner mitochondrial membrane.
What is the folded structure of the inner
mitochondrial membrane called? Cristae
,Question Answer
What is the importance of cristae on the inner
mitochondrial membrane? There is a great deal of surface area for the enzymes needed for oxidative phosphorylation.
Why does the mitochondria contain a loop of It contains the genes required for some of the enzymes involved in aerobic respiration. Mitochondria also contain
mitochondrial DNA? mitochondrial ribosomes which synthesise the proteins encoded by the mitochondrial DNA.
What type of cells contain a larger number of
mitochondria? Cells that require a large amount of energy e.g. muscle cells.
What is the structure of lysosomes? Specialised forms of vesicles that contain hydrolytic enzymes. They also have an internal acidic fluid.
Why do lysosomes have an acidic internal
fluid? As the lysosomal enzymes have an optimum pH which is acidic.
Digest pathogens in phagocytosis, can be used to destroy organelles that are no longer functional, can transfer
What are the functions of lysosomes? enzymes outside of cell by exocytosis
What does chromatin consist of? DNA coiled around proteins called histones.
What does nucleoplasm contain and what is It is a gelatinous substance inside the nucleus that contains molecules such as nucleotides and enzymes which are
its role? needed for DNA and RNA synthesis.
What does chromatin coil to form and when
are these structures visible? It coils to form chromosomes which only become visible when cells are preparing to divide.
Where ribosomal RNA is produced, which goes on to form part of the structure of ribosomes. The nucleolus is also
What is the function of the nucleolus? where ribosome subunits are assembled.
Vesicles are membranous sacs that have storage and transport roles. They consist of a single membrane with fluid
What is the structure and function of vesicles? inside.
Two layers of phospholipid molecules which contain a non-polar, hydrophobic region which is the two fatty acids,
and it contains a polar, hydrophillic region which is the phosphate group. Due to the hydrophobic nature of the fatty
What is the phospholipid bilayer composed of? acids, the hydrophillic phosphate group is on the exterior and interacts with the environment.
Partially permeable barriers between the cell and its environment, sites of some chemical reactions and also
What are the functions of cell membranes? involved in cell signalling through the diffusion of chemicals.
Why can hydrophobic molecules easily pass
through a phospholipid bilayer? Because the centre of the plasma membrane is hydrophobic and non-polar.
'Fluid' because phospholipid molecules can move around within each layer meaning the membrane is flexible and
Why is the structure of the plasma membrane can change shape. 'Mosaic' because the plasma membrane is studded with protein molecules and the size and
called the 'fluid mosaic model'? arrangement of these proteins varies, much like a mosaic pattern.
What other susbtances does the plasma
membrane contain? Proteins and cholesterol.
One end of the molecule is polar and hydrophillic, which attracts the polar head groups on the phospholipid
What is the structure of cholesterol in relation molecules. The rest of the molecule is non polar and hydrophobic meaning it attracts the non polar, hydrophobic
to hydrophobic and hydrophillic regions? fatty acids in the phospholipid molecules.
Why does the inclusion of cholesterol in the It increases the strength of it as it interacts with the phospholipids, making it more stable and less likely to be
plasma membrane do to it? damaged.
Reduces sideways movements of phospholipids and other molecules within the membrane. This means it controls
What does cholesterol help reduce in the the fluidity of the membrane, preventing it from becoming too fluid under warm conditions and too rigid under cool
plasma membrane? conditions.
Because the cholesterol packs the spaces
between the phospholipids, what does this
reduce? It reduces the movement of water soluble chemicals across the cell-surface membrane.
What are the three cytoskeletal fibres? (widest) Microtubules, intermediate fibres, microfilaments (narrowest)
What are microfilaments made of and what is They are narrow fibres containing the protein actin which can contract. They are involved in cell movement and also
their role? cell contraction during cytokinesis.
What are intermediate fibres made of and what
is their role? They are formed from a number of different proteins and their role is to strengthen the cell.
They are formed from subunits of the protein tubulin, and these subunits assemble to form tubulin polymers, then
What are microtubules made from? forming hollow microtubules.
They are involved in the movement of organelles, they form the spindle fibres that are involved in the movement of
chromosomes during mitosis and meiosis. Lastly, by forming a complex network in the cytoplasm, they help to
What are the functions of microtubules? determine the shape of a cell.
They are composed of a small and large subunit and are constructed of ribosomal RNA made in the nucleolus. They
What is the structure and function of are the sites of protein synthesis as they read the base sequence on the mRNA molecule and use this to order the
ribosomes? amino acids into the correct sequence.
Important in maintaining turgor in the cell so that the contents of the cell push against the cell wall. They do this as
they have a low water potential meaning water enters creating a hydrostatic pressure acting outwards, making the
What is the function of vacuoles? cell turgid.
It is a membrane lined sac in the cytoplasm. The membrane lining is called the tonoplast, and it is selectively
What is the structure of the vacuole? permeable meaning it controls which molecules enter and leave the vacuole.
What are vacuoles if they appear in animal
cells? They are small and transient (not permanent).
Where are chloroplasts not located? Roots
What is the membrane of chloroplasts like? It is a double membrane and it controls which molecules enter and leave the chloroplast.
Membrane bound flattened discs inside the chloroplast that stack to form grana. This is where the light dependent
What are thylakoids? reactions take place.
,Question Answer
Where the light dependent reactions of photosynthesis take place as they contain chlorophyll and enzymes
What is the role of thylakoids? needed.
What is several thylakoids stacked on top of
each other called? Granum
What is the benefit of stacking thylakoids into
grana? Allows light to be absorbed more efficiently.
What are thylakoids on different grana Flattened membranes called lamellae which play a role in light independent reactions and allow chemicals to be
connected by? passed between grana.
A fluid material inside chloroplasts and it is where the light independent reactions take place as it contains the
What is stroma and what is its role? enzymes needed.
What can the glucose produced by
photosynthesis be stored as in chloroplasts? Starch granules
What do chloroplasts contain that allows them They contain a loop of DNA which contains genes which encode for some of the proteins needed for
to synthesise proteins? photosynthesis. They also contain ribosomes which synthesise the proteins encoded by the DNA.
What is the cell wall made of? The polysaccharide cellulose
It is present in every plant cell and it provides strength to the plant cell as it needs to be mechanically strong enough
to resist the hydrostatic force of pressure water inflow. The contents of the cell also press against the cell wall,
making it turgid. It also acts as a defence mechanism, protecting the contents of the cell from invading
What is the function of the cell wall? pathogens.
What can cellulose molecules do to increase They form hydrogen bonds with each other to form larger structures called microfibrils. These form a mesh like
strength of cell wall? structure in the plant cell wall which is extremely strong.
What is the layer of material in between plant The middle lamella which contains polysaccharides as well as calcium and magnesium ions and this acts as a glue
cells called and what is its role? between plant cells.
Where are centrioles not found? Flowering plants and not found in most fungi
What are centrioles made of? Microtubules
What are a pair of centrioles called? Centrosome
They play a role in the assembly of the spindle fibres during mitosis and meiosis - however not essential for spindle
What are the functions of centrioles? assembly. Formation of cilia and flagella.
What is the structure of cilia and flagella? There are 9 pairs of microtubules with another pair in the centre (9+2 structure).
Using energy from ATP, the microtubule pairs can move relative to the pairs next to them, creating the bending
How can cilia and flagella move? motion of these organelles.
They are hairlike organelles that extend from the surface of certain cells. They beat in a ryhtmic manner to waft
matter (e.g. waft mucus in the trachea to the mouth to be swallowed). Stationary cilia play a role in sensing the
What are cilia and what are their functions? chemicals around the cell.
They are whiplike organelles that protrude from the surfaces of certain cells (e.g. sperm cells). Its role is to move the
What are flagella and what are their functions? cell.
What can the cell walls in algae contain? Cellulose and glycoproteins
What are the cell walls of fungi made of? Polysaccharide chitin as well as other polysaccharides and glycoproteins.
How wide is the diameter of a typical ribosome
in a human cell? Around 25 nanometres
What do early and modern light microscopes
have in common? They both have eyepiece lenses, stages and focusing dials.
What was the magnification of the first light
microscopes? Around 300 times
What can a modern light microscope magnify
to? Around 1000 times
What are the advantages of light microscopes We can use light microscopes to view living cells meaning we can explore processes such as cell division and
over other types of microscopes? movement of cells.
What is the problem with light microscopes? The problem of resolution due to the nature of light itself.
The minimum distance between two objects where they can still be seen as two seperate objects. The ability to
What is resolution? distinguish two objects as seperate entities.
What is the limit of resolution on standard light
microscopes? Around 200nm
What is the wavelength of visible light and how
does this affect the resolving power of light
microscopes? The wavelength of visible light is around 400nm to 700nm meaning it reduces the resolving power.
A laser scanning confocal microscope moves a laser across a specimen (point illumination), causing fluorescence
from structures labelled with a dye. The emitted light from the specimen is filtered through a pinhole aperture. The
What happens in laser scanning confocal beamsplitter is a dichroic mirror which reflects one wavelength of light (laser) but allows other wavelengths through
microscopy? (reflected light).
What are the advantages of laser scanning Higher resolution images than conventional light microscopy, can produce 3D images of cells, can visualise
confocal microscopy? specific proteins and structures within cells and watch them move. Non-invasive
Equation for magnification? Image size / actual size
Why is the resolution of electron microscopes
much better than light microscopes? Because electrons have a very short wavelength
, Question Answer
What is the maximum resolving power of
electron microscopes? 0.1nm
The interior of an electron microscope is a vacuum meaning we cannot view living samples. It also requires very
What are the disadvantages of electron careful staining and the specimen often has to be very thin. Can get artefacts (false images created by the staining
microscopes? process or the conditions inside the electron microscope). Expensive
The electron gun provides an electron beam. The inside of an electron microscope is a vacuum so the electrons can
pass through without bouncing of molecules in the air. We can focus the electron beam using electromagnetic
How do transmission electron microscopes lenses. The electron beam then passes through the specimen, producing flat 2D images and only works if specimen
work? is thinly sliced.
What are the advantages and disadvantages of
a TEM? + High resolution - Only works if specimen is thinly sliced, doesnt work on living organisms.
How does a scanning electron microscope In this microscope the electron beam doesn't pass through the specimen but rather scattered from the surface of
work? the specimen and detected.
What are the advantages and disadvantages of + can produce 3D images, specimen does not have to be thinly sliced - lower resolution than a TEM, specimen has
an SEM? to be coated with a metal, leading to potential artefacts.
What is the resolving power of an SEM? 3-10nm
The DNA is contained within a membrane bound nucleus. DNA is tightly wrapped around proteins called histones
which form chromosomes (means they can pack lots of DNA into tight space). Their DNA is a linear molecule
What are the features of eukaryotic cells? (doesnt form loop). Prescence of membrane bound organelles.
What are the ribosomes in eukaryotic cells? 80S
Where is extra chromosomal DNA found in
eukaryotic cells? Certain organelles such as chloroplasts and mitochondria.
How do eukaryotic cells reproduce compared Eukaryotic cells reproduce from asexual or sexual reproduction whereas prokaryotic cells reproduce through binary
to prokaryotic cells? fission.
Which are bigger: Eukaryotes or Prokaryotes? Eukaryotes
What are some key features of prokaryotic No membrane bound organelles at all - DNA is found in cytoplasm rather than nucleus. DNA is arranged into
cells? circular chromosome with no free ends - DNA not bound to histones.
Where is the extra chromsomal DNA found in
prokayotic cells? In small loops of DNA called plasmids.
What is the size of the ribosomes in
prokaryotic cells? 70S
What is the cell wall in bacteria made from? Peptidoglycan - polymer formed between peptides and polysaccharide molecules.
What is the role of the slime capsule on the
outside of the cell wall of bacterium? Can help protect the bacteria from phagocytosis by white blood cells.
They are fine protein strands on the surface of some bacteria and they help bacteria to attach to surfaces and also
What are pilli and what is their function? to other bacteria.
Why are lipid droplets and glycogen granules
important for bacteria? They act as nutrient stores for the bacterial cell.
Infoldings of the cell membrane of prokaryotic cells, however it is believed they are artefacts created when bacterial
What are mesosomes? cells are prepared for electron microscopy.
It is that mitochondria, chloroplasts and possibly other eukaryotic organelles were formally free living prokaryotes
(bacteria). The theory is that these prokaryotes were taken inside another cell as an endosymbiont - an organism
that lives within the body or cells of another organisms. This evenutally led to the evolution of eukaryotic
What is the theory of endosymbiosis? cells.
What is a stage micrometer? A microscope slide with a very accurate scale in micrometres engraved on it.
A glass disc marked with a fine scale of 1-100. The scale has no units and remains unchanged regardless of which
What is an eyepiece graticule? objective lens is being used.
The nucleus contains the genes for the protein needed in the form of DNA. The nucleus is the site of transcription,
where the base sequence of the gene for the protein is copied onto mRNA. mRNA leaves the nucleus through
nuclear pores. The ribosomes are then the sites of translation, these can be on the rough endoplasmic reticulum or
free. The base sequence of the mRNA allows the ribosome to assemble the chain of amino acids. The proteins are
then transported to the golgi apparatus in vesicles (enter cis fase, leave trans face) which are then modified and
Explain how organelles are interlinked for the repackaged into vesicles. These vesicles then fuse with the plasma membrane, with the contents of the vesicle
process of protein synthesis. being secreted by exocytosis.
What equipment is used to measure the
capacity of the lungs? Spirometer
What is meant by tidal volume? The volume of air that is inspired and expired with each resting breath.
The volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest
What is vital capacity? possible intake of breath.
What is inspiratory reserve volume? The maximum volume of air that you can breathe in over a normal inhalation.
The extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe
What is expiratory reserve volume? out.
What is residual volume? The volume of air that is left in your lungs when you have exhaled as hard as possible.
What is the role of ciliated epithelium? They contain cilia which beat back and forth to move the mucus (e.g. back to the mouth to be swallowed).
What is the role of goblet cells? They secrete mucus
