Biology Review
Paper 1:
• Cell Biology
• Organisation
• Infection and response
• Bioenergetics
Paper 2:
• Homeostasis and response
• Inheritance, variation and evolution
• Ecology
Cell Biology:
Prokaryotic cells Both Eukaryotic cells
• Free organelles • Plasma membrane • Contain membrane-bound
• Nuculids • Ribosomes organelles
• Bacteria • Cytoplasm • Have a nucleus
• Smaller • Plants, animals and fungi
• Binary fusion • Bigger
• Plasmids • Mitosis or miosis
Animal cells:
Nucleus- contains the genetic material that controls the activities of the cell
Mitochondria- the sight of aerobic respiration in the cell, giving the cell energy
Cytoplasm- a gel like surface where most of the chemical reactions in the cell
occur, (also contains enzymes that control these reactions)
Cell membrane- regulates what substances come in and out of the cell
Ribosomes- where proteins are made in the cell
Plant cells:
Cell wall- the structure around a plant cell, which supports the cell and is
made of cellulose
Permanent vacuole: contains cell sap and a weak solution of sugar and salts
Chloroplast- the location of photosynthesis in a plant cell (making food for the
plant), it also contains chlorophyll; the green substance needed to absorb light
for photosynthesis
Cell differentiation and specialisation:
A specialised is one that has differed from a normal cell to perform a specific task.
Cell differentiation is the process by which a cell becomes specialised.
Animals and plants produced by sexual reproduction begin life as a single cell – a fertilised egg (a zygote).
This cell must divide to produce a multicellular organism. It must also differentiate so that its cells
develop features that enable them to fulfil specific roles.
,Examples:
Sperm cell:
1. Streamlined head to swim more efficiently
2. Long tail to swim faster
3. Lots of mitochondria to have enough energy to swim to the egg
4. Enzymes in the head to digest through the egg cell membrane
Nerve cell:
1. Specialised to rapidly carry signal from one end of the body to another
2. Myelin sheath acts as an insulator around a wire carrying the signal out faster
3. Have branched connections to contact multiple cells
Muscle cells:
1. The function of a muscle cell is to contract quickly
2. The cells are long to contract easily
3. Contain lots of mitochondria needed for movement
Root hair cell (in plants):
1. Grow into long hairs meaning more surface area to absorb water
2. Thin cell wall to absorb more water
Cells of the Specialisation
Leaf Palisade mesophyll Carry out photosynthesis
Spongy mesophyll Allow gases to circulate for the exchange of gases between the leaf and the
environment, carry out some photosynthesis
Guard cells Open and close to control the exchange of gases – carbon dioxide, water
vapour and oxygen
Phloem Sieve tubes Transport products of photosynthesis, including sugars and amino acids,
from the leaf to where they are needed
Companion cells Provide the energy required for transporting substances in sieve tubes
Xylem Xylem vessels Transport water and dissolved minerals from the roots, up the plant
Growing points Meristem Produce new cells as they divide
Microscopy:
Light microscope: use lights and lenses to magnify an image; they let us see individual
cells and large organelles
Electron microscope: use electrons instead of light to create the image; they are more
powerful than light microscopes, even allowing you to see smaller organelles such as
ribosomes
1. Start clipping slide onto the stage
2. Select the lowest powered objective lenses
3. Use the coarse adjustment nob to move the stage to the right position
4. Use the eye piece and coarse adjustment to roughly focus the image
5. Adjust the fine focus knob to get a clearer image
6. Change to a more detailed lens if you want more magnification
Culturing microorganisms:
Bacteria cells can multiply up to every 20 minutes depending on the temperature and
the nutrients they have. They can be grown in a broth solution or as colonies on an
agar gel plate
,Cell division:
Chromosomes: The nucleus of a cell contains chromosomes carrying genetic
molecules in a molecule called DNA. Each human cell contains 46 chromosomes,
arranged in 23 pairs; the 23rd pair of chromosome controls the humans’ sex
DNA: deoxyribonucleic acid, the material inside a nucleus of cells carrying the
genetic information of the organism
Gene: a section of DNA which controls the cells chemistry, mainly protein
production
𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑐𝑒𝑙𝑙𝑠 𝑖𝑛 𝑠𝑡𝑎𝑔𝑒
𝑙𝑒𝑔𝑛𝑡ℎ 𝑜𝑓 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑝ℎ𝑎𝑠𝑒 = ∗ 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑐𝑒𝑙𝑙 𝑐𝑦𝑐𝑙𝑒
𝑡𝑜𝑡𝑎𝑙 𝑐𝑒𝑙𝑙𝑠
Mitosis:
1. Before a cell can divide it needs to grow and increase the number of
sub-cellular structures such as ribosomes and mitochondria. The DNA
replicates to form two copies of each chromosome.
2. In mitosis one set of chromosomes is pulled to each end of the cell and
the nucleus divides.
3. Finally, the cytoplasm and cell membranes divide to form two identical cells
Stem cells: an undifferentiated cell of an organism which is capable of giving rise to more cells of the
same type and from which other cells arise from differentiation.
• Stem cells from human embryos can be cloned and made to differentiate into most
different types of human cells. Stem cells from adult bone marrow can form many
types of cells including blood cells. stem cells from a human embryo can produce a
wider range of cell types. Therapeutic cloning: both these cells can be used to
replace cells that have been damaged or destroyed (e.g. type 1 diabetes, multiple
sclerosis and spinal cord or brain injury). Using embryotic cells raises ethical issues
and challenges
• Stem cells in a plant are found in the meristem in a growing shoot, new
cells are being produced continuously near the tip. As the cells become
older, further away from the tip, they become differentiated – they enlarge
and develop vacuoles; these cells can be removed from a plant and can be
used to clone it in a tissue culture, providing support and water for living
cells along with nutrients and hormones to stimulate growth. Plants are
cloned to produce identical plants quickly and economically.
Benefits and risks associated with the use of stem cells in medicine
Clinical issues Ethical issues Social issues
• No guaranty treatment will • A source of embryonic stem • Educating the public about
work cells is unused embryos what stem cells can, and can't
• Hard to find suitable donors produced by in do, is important.
• Hard to obtain and store said vitro fertilisation (IVF) • Whether the benefits of stem
stem cells, which would have • For therapeutic cloning is it cell use outweigh the
to be collected before birth right to create embryos for objections.
• Mutations can occur in therapy, and destroy them in • Much of the research is being
cultured stem cells the process? carried out by commercial
• Stem cells may be • Embryos could come to be clinics, so reported successes
contaminated with viruses viewed as a commodity, and are not subject to peer review.
not as an embryo that could Patients could be exploited by
develop into a person. paying for expensive
• At what stage of its treatments and being given
development should an false hope of a cure as stem
embryo be regarded as, and cell therapies are only in their
treated as a person? developmental stages.
, Transport in cells:
Substances move in and out of a cell via diffusion (oxygen and carbon dioxide into and out of plant leaf
and lungs and urea from cells into the blood plasma), active transport (mineral ions, sugar molecules into
the blood from the gut) and osmosis (water).
Diffusion: The movement of fluids from an area of higher concentration to an area of lower
concentration. Following concentration gradient.
Factor Reason
The concentration gradient The greater the difference in concentration, the quicker the rate of diffusion.
The temperature The higher the temperature, the more kinetic energy the particles will have, so
they will move and mix more quickly.
The surface area of the cell The greater the surface area, the faster the rate of diffusion.
membrane separating the
different regions
Osmosis: Osmosis is the diffusion of water molecules, from a region where the water molecules are in
higher concentration, to a region where they are in lower concentration, through a partially
permeable membrane (e.g. root hair cells absorbing water). When cells experience a high or low
concertation of water it causes them to expand or shrivel.
60 𝑚𝑖𝑛𝑠
𝑊𝑎𝑡𝑒𝑟 𝑢𝑝𝑡𝑎𝑘𝑒 𝑖𝑛 𝑎𝑛 ℎ𝑜𝑢𝑟 = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑚𝑎𝑠𝑠 ∗
𝑡𝑖𝑚𝑒 𝑖𝑛 𝑚𝑖𝑛𝑠
Animal Plant
Hypertonic/ high Hypotonic/ dilute Hypertonic/ high Hypotonic/ dilute
concentration concentration
Water leaves the cell Water enter the cell Water leaves the cell Water enter the cell
causing it to shrivel known causing it to fill then burst causing it to causing it to fill but
as crenation know as cell lysis shrivel known as doesn’t burst due to the
flaccid cell wall known as turgid
Cell contents pull away Cell contents push against
from wall its wall
In a very concentrated
solution, the
cell undergoes
full
plasmolysis as
the cells lose more water.
Active transport: the movement of molecules from low to high concentration through the use of energy.
Against concentration gradient (root hair cells absorbing nutrients, glucose molecules in animals moving
across the gut so all glucose can be absorbed)
Process Descriptions Substances moved Energy
required
Diffusion Substances move from a high to a low Carbon dioxide, oxygen, water, food No
concentration down a concentration gradient substances, wastes, e.g. urea
Osmosis Water moves from a high to a low Water No
concentration across a partially permeable
membrane and down a concentration gradient
Active Substances move against a concentration Mineral ions into plant roots, glucose Yes
transport gradient from the gut into intestinal cells, from
where it moves into the blood
Paper 1:
• Cell Biology
• Organisation
• Infection and response
• Bioenergetics
Paper 2:
• Homeostasis and response
• Inheritance, variation and evolution
• Ecology
Cell Biology:
Prokaryotic cells Both Eukaryotic cells
• Free organelles • Plasma membrane • Contain membrane-bound
• Nuculids • Ribosomes organelles
• Bacteria • Cytoplasm • Have a nucleus
• Smaller • Plants, animals and fungi
• Binary fusion • Bigger
• Plasmids • Mitosis or miosis
Animal cells:
Nucleus- contains the genetic material that controls the activities of the cell
Mitochondria- the sight of aerobic respiration in the cell, giving the cell energy
Cytoplasm- a gel like surface where most of the chemical reactions in the cell
occur, (also contains enzymes that control these reactions)
Cell membrane- regulates what substances come in and out of the cell
Ribosomes- where proteins are made in the cell
Plant cells:
Cell wall- the structure around a plant cell, which supports the cell and is
made of cellulose
Permanent vacuole: contains cell sap and a weak solution of sugar and salts
Chloroplast- the location of photosynthesis in a plant cell (making food for the
plant), it also contains chlorophyll; the green substance needed to absorb light
for photosynthesis
Cell differentiation and specialisation:
A specialised is one that has differed from a normal cell to perform a specific task.
Cell differentiation is the process by which a cell becomes specialised.
Animals and plants produced by sexual reproduction begin life as a single cell – a fertilised egg (a zygote).
This cell must divide to produce a multicellular organism. It must also differentiate so that its cells
develop features that enable them to fulfil specific roles.
,Examples:
Sperm cell:
1. Streamlined head to swim more efficiently
2. Long tail to swim faster
3. Lots of mitochondria to have enough energy to swim to the egg
4. Enzymes in the head to digest through the egg cell membrane
Nerve cell:
1. Specialised to rapidly carry signal from one end of the body to another
2. Myelin sheath acts as an insulator around a wire carrying the signal out faster
3. Have branched connections to contact multiple cells
Muscle cells:
1. The function of a muscle cell is to contract quickly
2. The cells are long to contract easily
3. Contain lots of mitochondria needed for movement
Root hair cell (in plants):
1. Grow into long hairs meaning more surface area to absorb water
2. Thin cell wall to absorb more water
Cells of the Specialisation
Leaf Palisade mesophyll Carry out photosynthesis
Spongy mesophyll Allow gases to circulate for the exchange of gases between the leaf and the
environment, carry out some photosynthesis
Guard cells Open and close to control the exchange of gases – carbon dioxide, water
vapour and oxygen
Phloem Sieve tubes Transport products of photosynthesis, including sugars and amino acids,
from the leaf to where they are needed
Companion cells Provide the energy required for transporting substances in sieve tubes
Xylem Xylem vessels Transport water and dissolved minerals from the roots, up the plant
Growing points Meristem Produce new cells as they divide
Microscopy:
Light microscope: use lights and lenses to magnify an image; they let us see individual
cells and large organelles
Electron microscope: use electrons instead of light to create the image; they are more
powerful than light microscopes, even allowing you to see smaller organelles such as
ribosomes
1. Start clipping slide onto the stage
2. Select the lowest powered objective lenses
3. Use the coarse adjustment nob to move the stage to the right position
4. Use the eye piece and coarse adjustment to roughly focus the image
5. Adjust the fine focus knob to get a clearer image
6. Change to a more detailed lens if you want more magnification
Culturing microorganisms:
Bacteria cells can multiply up to every 20 minutes depending on the temperature and
the nutrients they have. They can be grown in a broth solution or as colonies on an
agar gel plate
,Cell division:
Chromosomes: The nucleus of a cell contains chromosomes carrying genetic
molecules in a molecule called DNA. Each human cell contains 46 chromosomes,
arranged in 23 pairs; the 23rd pair of chromosome controls the humans’ sex
DNA: deoxyribonucleic acid, the material inside a nucleus of cells carrying the
genetic information of the organism
Gene: a section of DNA which controls the cells chemistry, mainly protein
production
𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑐𝑒𝑙𝑙𝑠 𝑖𝑛 𝑠𝑡𝑎𝑔𝑒
𝑙𝑒𝑔𝑛𝑡ℎ 𝑜𝑓 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑝ℎ𝑎𝑠𝑒 = ∗ 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑐𝑒𝑙𝑙 𝑐𝑦𝑐𝑙𝑒
𝑡𝑜𝑡𝑎𝑙 𝑐𝑒𝑙𝑙𝑠
Mitosis:
1. Before a cell can divide it needs to grow and increase the number of
sub-cellular structures such as ribosomes and mitochondria. The DNA
replicates to form two copies of each chromosome.
2. In mitosis one set of chromosomes is pulled to each end of the cell and
the nucleus divides.
3. Finally, the cytoplasm and cell membranes divide to form two identical cells
Stem cells: an undifferentiated cell of an organism which is capable of giving rise to more cells of the
same type and from which other cells arise from differentiation.
• Stem cells from human embryos can be cloned and made to differentiate into most
different types of human cells. Stem cells from adult bone marrow can form many
types of cells including blood cells. stem cells from a human embryo can produce a
wider range of cell types. Therapeutic cloning: both these cells can be used to
replace cells that have been damaged or destroyed (e.g. type 1 diabetes, multiple
sclerosis and spinal cord or brain injury). Using embryotic cells raises ethical issues
and challenges
• Stem cells in a plant are found in the meristem in a growing shoot, new
cells are being produced continuously near the tip. As the cells become
older, further away from the tip, they become differentiated – they enlarge
and develop vacuoles; these cells can be removed from a plant and can be
used to clone it in a tissue culture, providing support and water for living
cells along with nutrients and hormones to stimulate growth. Plants are
cloned to produce identical plants quickly and economically.
Benefits and risks associated with the use of stem cells in medicine
Clinical issues Ethical issues Social issues
• No guaranty treatment will • A source of embryonic stem • Educating the public about
work cells is unused embryos what stem cells can, and can't
• Hard to find suitable donors produced by in do, is important.
• Hard to obtain and store said vitro fertilisation (IVF) • Whether the benefits of stem
stem cells, which would have • For therapeutic cloning is it cell use outweigh the
to be collected before birth right to create embryos for objections.
• Mutations can occur in therapy, and destroy them in • Much of the research is being
cultured stem cells the process? carried out by commercial
• Stem cells may be • Embryos could come to be clinics, so reported successes
contaminated with viruses viewed as a commodity, and are not subject to peer review.
not as an embryo that could Patients could be exploited by
develop into a person. paying for expensive
• At what stage of its treatments and being given
development should an false hope of a cure as stem
embryo be regarded as, and cell therapies are only in their
treated as a person? developmental stages.
, Transport in cells:
Substances move in and out of a cell via diffusion (oxygen and carbon dioxide into and out of plant leaf
and lungs and urea from cells into the blood plasma), active transport (mineral ions, sugar molecules into
the blood from the gut) and osmosis (water).
Diffusion: The movement of fluids from an area of higher concentration to an area of lower
concentration. Following concentration gradient.
Factor Reason
The concentration gradient The greater the difference in concentration, the quicker the rate of diffusion.
The temperature The higher the temperature, the more kinetic energy the particles will have, so
they will move and mix more quickly.
The surface area of the cell The greater the surface area, the faster the rate of diffusion.
membrane separating the
different regions
Osmosis: Osmosis is the diffusion of water molecules, from a region where the water molecules are in
higher concentration, to a region where they are in lower concentration, through a partially
permeable membrane (e.g. root hair cells absorbing water). When cells experience a high or low
concertation of water it causes them to expand or shrivel.
60 𝑚𝑖𝑛𝑠
𝑊𝑎𝑡𝑒𝑟 𝑢𝑝𝑡𝑎𝑘𝑒 𝑖𝑛 𝑎𝑛 ℎ𝑜𝑢𝑟 = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑚𝑎𝑠𝑠 ∗
𝑡𝑖𝑚𝑒 𝑖𝑛 𝑚𝑖𝑛𝑠
Animal Plant
Hypertonic/ high Hypotonic/ dilute Hypertonic/ high Hypotonic/ dilute
concentration concentration
Water leaves the cell Water enter the cell Water leaves the cell Water enter the cell
causing it to shrivel known causing it to fill then burst causing it to causing it to fill but
as crenation know as cell lysis shrivel known as doesn’t burst due to the
flaccid cell wall known as turgid
Cell contents pull away Cell contents push against
from wall its wall
In a very concentrated
solution, the
cell undergoes
full
plasmolysis as
the cells lose more water.
Active transport: the movement of molecules from low to high concentration through the use of energy.
Against concentration gradient (root hair cells absorbing nutrients, glucose molecules in animals moving
across the gut so all glucose can be absorbed)
Process Descriptions Substances moved Energy
required
Diffusion Substances move from a high to a low Carbon dioxide, oxygen, water, food No
concentration down a concentration gradient substances, wastes, e.g. urea
Osmosis Water moves from a high to a low Water No
concentration across a partially permeable
membrane and down a concentration gradient
Active Substances move against a concentration Mineral ions into plant roots, glucose Yes
transport gradient from the gut into intestinal cells, from
where it moves into the blood
