Cell Biology
Cell structure –
- Animal and plant cells are examples of eukaryotes. Bacteria are prokaryotes.
- Cells are the smallest unit of life that can replicate independently.
- Eukaryotes divide to make more of themselves, usually for growth and repair (of dead cells).
Prokaryotes (bacteria) are a whole organism and replicate through asexual reproduction.
- An adult contains over 40 trillion cells in their body.
- Parts of a cell are subcellular structures/organelles.
- Both animal and plant cells are surrounded by a cell membrane (controls which substances
pass in and out of the cell), a nucleus (contains genetic material / DNA, controls activity of cell),
a cytoplasm (where chemical reactions take place, jelly-like material with nutrients and salts),
mitochondria (site of aerobic respiration, release energy for the cell) and lots of ribosomes
(protein synthesis).
- Plant cells also have a rigid cell wall made up of cellulose (provides support and structure to
prevent bursting). They have a permanent vacuole (contains cell sap, a mix of sugar, salts and
water, helps maintain structure/shape of cell). They have chloroplasts (where photosynthesis
occurs, substance called chlorophyll making plants green).
- Bacteria consist of a single prokaryotic cell (unicellular as 1 cell organism). They are smaller
than animal/plant cells. They have a cytoplasm, cell wall, cell membrane, ribosomes. They have
circular strands of DNA (or circular chromosome, nucleoid) floating around that contain genes
they need to survive and reproduce. Some also have additional rings known as plasmids which
contain extra genes (e.g. antibiotic resistance). They have flagella (thread-like structures
protruding out that can rotate to propel the bacteria).
Microscopy -
- The base is at the bottom, with the arm connecting the microscope. There is a light source
(e.g. actual light, mirror). Above it is a stage with a microscope slide on. We have 3 objective
lenses (different magnifications e.g. 10x, 20x, 50x). An eyepiece lens has a fixed magnification.
The body tube is the bulk of it. It has a coarse and fine focusing knob to get the image in focus.
- The term object refers to the real object or sample that you’re looking at. The image is what
we seen when looking down a microscope.
- Light hits the mirror and reflects through the object, passing into the objective lens, eyepiece
lens and into our eye. The lenses spread out the light rays so the image is magnified.
- Magnification is how many times larger the image is than the object.
- Magnification = Image Size / Object Size.
- Resolution is the shortest distance between two points on an object that can still be
distinguished as two separate entities (how detailed it is).
- A light microscope is used in a classroom. They are small, easy to use, and relatively cheap.
However because they rely on light, their resolution is limited to 0.2um (any details less than this
,will appear blurry). They’re not good enough to study subcellular structures.
- Electron microscopes are very expensive, very big and hard to use (used by scientists in
laboratories). They use electrons instead of light so have a lower wavelength and a better
resolution (2000x better than light), so can be used to study sub cellular structures. However,
they can only be used on dead/inactive samples and are only in black and white.
nm ------------- um ------------- mm --- cm ---------- m ------------- km
- We divide by 1000 moving right along this, or multiply by 1000 going left.
- mm à cm divided by 10 //// cm à m divided by 100.
- nm = nanometers //// um = micrometers
- Atoms range from around 0.1-0.5nm in diameter. Glucose is about 1nm. Viruses are 100nm.
Bacteria is 1um. Animal/plant cells are 10-100um. Human hair is 100um wide.
- With the naked human eye we can see to approx. 100um small. A light microscope can see
down to 500nm. An electron microscope can see down to 0.1nm.
Mitosis -
- All multicellular eukaryotic organisms require a continuous supply of new cells for growth,
development and repair. The skin cells continuously fall off our bodies.
- The cell cycle is the life cycle of the cell. It contains growth, DNA replication + mitosis and
division (cytokinesis).
- In the first step, the cell grows in size and increases the number of sub-cellular structures
such as mitochondria and ribosomes. Next, the DNA is duplicated so the two new cells each
have a full set.
- When a cell is not dividing, DNA is spread out on long strings, however once it prepares for
division it condenses into chromosomes (coiled up packets of DNA, contain genes and control
characteristics). Eukaryotics have 2 copies of each chromosome, with a total of 23 pairs (46).
Other species have different numbers of chromosomes. It duplicates each chromosome (stays
attached to original) and forms an X shape (has ‘arms’).
- Once the cell is ready to divide all 46 chromosomes line up in the centre. Cell fibres pull the
arms to opposite sides of the cell (poles). It breaks the chromosomes in half.
- The cell membrane and cytoplasm pull apart forming 2 daughter cells. Each cell has the same
DNA and are ‘identical’ to each other and the parent cell.
Binary Fission -
- Binary fission is the process by which prokaryotic organisms (e.g. bacteria) divide and
reproduce. It is different to mitosis and meiosis.
- It is not only a type of cell division, but also asexual reproduction.
- Before a bacteria cell can divide it has to grow and replicate all its genetic material. The two
large circular strands move to either side, however the plasmids are arranged randomly. It
grows a new cell wall down the middle, allows the halves to pull apart.
- Because binary fission is simple and quick (some every 20 minutes), populations grow very
quickly. Mean division time is the average time it takes for a bacteria cell to divide. This depends
on the species and the conditions (they like it to be warm, moist and with plenty of nutrients).
Without these it could divide slowly or not at all.
,
Stem Cells -
- Stem cells are able to differentiate into specialised cells and able to divide by mitosis to form
more cells. Undifferentiated cells.
- Embryonic stem cells can differentiate into any type of cell. They are a zygote formed from an
egg and sperm that divide by mitosis to form an embryo.
- Adult stem cells are already specialised, so can only differentiate into a narrow range of cells.
Bone marrow contain adult stem cells but can only become different types of blood cells
(platelets, white blood cells, red blood cells). They don’t form new tissues but can replace.
- Plant stem cells are found in plant tissues called ‘meristems’, found in areas that are
continuously growing (shoots, roots). They differentiate into all the cells it needs (e.g. phloem,
xylem, palisade, root hair). They assist for a plant’s entire life. They can undifferentiate after
becoming a specific cell type.
Specialised Cells + Differentiation -
- Specialised cells have a specific role in the body, with a specific shape or structure to help
them fulfil it.
- Specialised cells in humans include nerve cells, muscle cells and sperm cells. In plants this
includes root hair cells, phloem cells and xylem cells.
- A sperm cell delivers genetic material to an egg to fertilise it. Adaptations: Half as many
genetic material as adult cell, flagellum so the cell can swim through the uterus and fallopian
tube, has lots of mitochondria for energy and is streamlined. They have lots of digestive
enzymes at the front to break a hole into the egg.
- Differentiation is the process by which cells become specialised.
- Red blood cells don’t have a nucleus to make more room to carry oxygen.
- Nerve cells conduct electrical impulses. They have branches called dendrites allowing them to
connect with other cells. The tail is an axon (long, conducts electrical impulses in one direction).
A myelin sheath insulates the electrical impulse. Synapses send neurotransmitter chemicals to
another nerve cell or effector.
- Cardiac muscle contracts automatically. We control our skeletal muscles. Special proteins that
slide past each other make muscle fibres contract. Many mitochondria to transfer energy for
these contractions. Glycogen to ‘store’ energy in the form of glucose.
- Plant cells have a cell wall, vacuole and chloroplasts. Root hair cells absorb water and mineral
ions and transfer them into the plant. They have a long hair like extension to increase the
surface area for absorption. They enter through active transport requiring many mitochondria.
They have a large permanent vacuole for water to move into by osmosis. They don’t have
chloroplasts (no need).
- Xylem cells transport water and mineral ions from the roots to the leaves. They are made from
cells that have died. Cell wall broke down forming hollow tubes strengthened by lignin. The
movement through xylem cells is known as the transpiration stream.
- Phloem cells transport the products of photosynthesis (glucose) from the leaves to the rest of
the plant. Made from living cells where cell wall broken down to form sieve plates that allow
sugars to flow freely by translocation. Companion cells are found either side of phloem cells that
Cell structure –
- Animal and plant cells are examples of eukaryotes. Bacteria are prokaryotes.
- Cells are the smallest unit of life that can replicate independently.
- Eukaryotes divide to make more of themselves, usually for growth and repair (of dead cells).
Prokaryotes (bacteria) are a whole organism and replicate through asexual reproduction.
- An adult contains over 40 trillion cells in their body.
- Parts of a cell are subcellular structures/organelles.
- Both animal and plant cells are surrounded by a cell membrane (controls which substances
pass in and out of the cell), a nucleus (contains genetic material / DNA, controls activity of cell),
a cytoplasm (where chemical reactions take place, jelly-like material with nutrients and salts),
mitochondria (site of aerobic respiration, release energy for the cell) and lots of ribosomes
(protein synthesis).
- Plant cells also have a rigid cell wall made up of cellulose (provides support and structure to
prevent bursting). They have a permanent vacuole (contains cell sap, a mix of sugar, salts and
water, helps maintain structure/shape of cell). They have chloroplasts (where photosynthesis
occurs, substance called chlorophyll making plants green).
- Bacteria consist of a single prokaryotic cell (unicellular as 1 cell organism). They are smaller
than animal/plant cells. They have a cytoplasm, cell wall, cell membrane, ribosomes. They have
circular strands of DNA (or circular chromosome, nucleoid) floating around that contain genes
they need to survive and reproduce. Some also have additional rings known as plasmids which
contain extra genes (e.g. antibiotic resistance). They have flagella (thread-like structures
protruding out that can rotate to propel the bacteria).
Microscopy -
- The base is at the bottom, with the arm connecting the microscope. There is a light source
(e.g. actual light, mirror). Above it is a stage with a microscope slide on. We have 3 objective
lenses (different magnifications e.g. 10x, 20x, 50x). An eyepiece lens has a fixed magnification.
The body tube is the bulk of it. It has a coarse and fine focusing knob to get the image in focus.
- The term object refers to the real object or sample that you’re looking at. The image is what
we seen when looking down a microscope.
- Light hits the mirror and reflects through the object, passing into the objective lens, eyepiece
lens and into our eye. The lenses spread out the light rays so the image is magnified.
- Magnification is how many times larger the image is than the object.
- Magnification = Image Size / Object Size.
- Resolution is the shortest distance between two points on an object that can still be
distinguished as two separate entities (how detailed it is).
- A light microscope is used in a classroom. They are small, easy to use, and relatively cheap.
However because they rely on light, their resolution is limited to 0.2um (any details less than this
,will appear blurry). They’re not good enough to study subcellular structures.
- Electron microscopes are very expensive, very big and hard to use (used by scientists in
laboratories). They use electrons instead of light so have a lower wavelength and a better
resolution (2000x better than light), so can be used to study sub cellular structures. However,
they can only be used on dead/inactive samples and are only in black and white.
nm ------------- um ------------- mm --- cm ---------- m ------------- km
- We divide by 1000 moving right along this, or multiply by 1000 going left.
- mm à cm divided by 10 //// cm à m divided by 100.
- nm = nanometers //// um = micrometers
- Atoms range from around 0.1-0.5nm in diameter. Glucose is about 1nm. Viruses are 100nm.
Bacteria is 1um. Animal/plant cells are 10-100um. Human hair is 100um wide.
- With the naked human eye we can see to approx. 100um small. A light microscope can see
down to 500nm. An electron microscope can see down to 0.1nm.
Mitosis -
- All multicellular eukaryotic organisms require a continuous supply of new cells for growth,
development and repair. The skin cells continuously fall off our bodies.
- The cell cycle is the life cycle of the cell. It contains growth, DNA replication + mitosis and
division (cytokinesis).
- In the first step, the cell grows in size and increases the number of sub-cellular structures
such as mitochondria and ribosomes. Next, the DNA is duplicated so the two new cells each
have a full set.
- When a cell is not dividing, DNA is spread out on long strings, however once it prepares for
division it condenses into chromosomes (coiled up packets of DNA, contain genes and control
characteristics). Eukaryotics have 2 copies of each chromosome, with a total of 23 pairs (46).
Other species have different numbers of chromosomes. It duplicates each chromosome (stays
attached to original) and forms an X shape (has ‘arms’).
- Once the cell is ready to divide all 46 chromosomes line up in the centre. Cell fibres pull the
arms to opposite sides of the cell (poles). It breaks the chromosomes in half.
- The cell membrane and cytoplasm pull apart forming 2 daughter cells. Each cell has the same
DNA and are ‘identical’ to each other and the parent cell.
Binary Fission -
- Binary fission is the process by which prokaryotic organisms (e.g. bacteria) divide and
reproduce. It is different to mitosis and meiosis.
- It is not only a type of cell division, but also asexual reproduction.
- Before a bacteria cell can divide it has to grow and replicate all its genetic material. The two
large circular strands move to either side, however the plasmids are arranged randomly. It
grows a new cell wall down the middle, allows the halves to pull apart.
- Because binary fission is simple and quick (some every 20 minutes), populations grow very
quickly. Mean division time is the average time it takes for a bacteria cell to divide. This depends
on the species and the conditions (they like it to be warm, moist and with plenty of nutrients).
Without these it could divide slowly or not at all.
,
Stem Cells -
- Stem cells are able to differentiate into specialised cells and able to divide by mitosis to form
more cells. Undifferentiated cells.
- Embryonic stem cells can differentiate into any type of cell. They are a zygote formed from an
egg and sperm that divide by mitosis to form an embryo.
- Adult stem cells are already specialised, so can only differentiate into a narrow range of cells.
Bone marrow contain adult stem cells but can only become different types of blood cells
(platelets, white blood cells, red blood cells). They don’t form new tissues but can replace.
- Plant stem cells are found in plant tissues called ‘meristems’, found in areas that are
continuously growing (shoots, roots). They differentiate into all the cells it needs (e.g. phloem,
xylem, palisade, root hair). They assist for a plant’s entire life. They can undifferentiate after
becoming a specific cell type.
Specialised Cells + Differentiation -
- Specialised cells have a specific role in the body, with a specific shape or structure to help
them fulfil it.
- Specialised cells in humans include nerve cells, muscle cells and sperm cells. In plants this
includes root hair cells, phloem cells and xylem cells.
- A sperm cell delivers genetic material to an egg to fertilise it. Adaptations: Half as many
genetic material as adult cell, flagellum so the cell can swim through the uterus and fallopian
tube, has lots of mitochondria for energy and is streamlined. They have lots of digestive
enzymes at the front to break a hole into the egg.
- Differentiation is the process by which cells become specialised.
- Red blood cells don’t have a nucleus to make more room to carry oxygen.
- Nerve cells conduct electrical impulses. They have branches called dendrites allowing them to
connect with other cells. The tail is an axon (long, conducts electrical impulses in one direction).
A myelin sheath insulates the electrical impulse. Synapses send neurotransmitter chemicals to
another nerve cell or effector.
- Cardiac muscle contracts automatically. We control our skeletal muscles. Special proteins that
slide past each other make muscle fibres contract. Many mitochondria to transfer energy for
these contractions. Glycogen to ‘store’ energy in the form of glucose.
- Plant cells have a cell wall, vacuole and chloroplasts. Root hair cells absorb water and mineral
ions and transfer them into the plant. They have a long hair like extension to increase the
surface area for absorption. They enter through active transport requiring many mitochondria.
They have a large permanent vacuole for water to move into by osmosis. They don’t have
chloroplasts (no need).
- Xylem cells transport water and mineral ions from the roots to the leaves. They are made from
cells that have died. Cell wall broke down forming hollow tubes strengthened by lignin. The
movement through xylem cells is known as the transpiration stream.
- Phloem cells transport the products of photosynthesis (glucose) from the leaves to the rest of
the plant. Made from living cells where cell wall broken down to form sieve plates that allow
sugars to flow freely by translocation. Companion cells are found either side of phloem cells that
