GCSE Biology: Cell Biology Revision Notes
Eukaryotes and Prokaryotes:
● All living things are made up of cells which are eukaryotes or prokaryotes
● Eukaryotes: Plant and Animal cells have a cell membrane, cytoplasm and genetic material in a
nucleus
● Prokaryotes: Bacterial cells are much smaller and have cytoplasm and a cell membrane surrounded
by a cell wall and the genetic material is found in a single DNA loop and small DNA rings called
plasmids
Animal and plant cells:
● Animal cells have: nucleus, cytoplasm, cell membrane, mitochondria and ribosomes
● Plant cells have: nucleus, cytoplasm, cell membrane, cell wall, a permanent vacuole, chloroplasts,
mitochondria and ribosomes
● Nucleus - Contains genetic material that controls the activities of the cell
● Cytoplasm - Where chemical reactions take place
● Cell membrane - Controls what enters and leaves the cell. It also holds the cell together.
● Cell wall - Made of cellulose. Supports and strengthens the cell
● Permanent vacuole - Contains cell sap and keeps the cell turgid
● Chloroplasts - Where photosynthesis takes place
● Mitochondria - Where respiration takes place
● Ribosomes - Where protein synthesis takes place
● Plasmids - Small rings of DNA
Cell specialisation:
● Sperm cells: Deliver male DNA to the egg cell where the female DNA is located
○ It has a long tail and streamlined head to help it swim to the egg
○ There are a lot of mitochondria to provide energy for the cell
○ It carries enzymes in its head to digest through the egg membrane
● Nerve cells: Carry electrical impulses from one part of the body to another
○ They have a long axon to carry the impulse over a long distance
○ They have branched connections at both ends to connect to other nerve cells
○ They are insulated in a fatty sheath which helps the impulse move along the nerve quicker
● Muscle cells: Contract quickly for movement
○ They have a lot of mitochondria to provide energy for contraction
○ They have protein filaments which slide over each other for contraction
● Root hair cells: Absorb water and minerals
○ Root hairs increase surface area so the rate of water uptake by osmosis is greater
○ They have thin walls so water can move easily due to a short diffusion distance
○ Mitochondria release energy for active transport of mineral ions
● Xylem cells: Transports water and dissolved minerals
○ The cells are dead and hollow forming hollow tubes which allows water to be drawn
upwards
○ Cells have no organelles to allow water to be drawn upwards
○ Outer walls are strengthened by lignin which thickens it and supports the plant
● Phloem cells: Transports dissolved sugars and amino acids
○ Cells are joined end to end and contain sieve plates with holes to form tubes which allow
amino acids and sugars to flow easily
○ They are living but have few subcellular organisms to allow amino acids and sugars to flow
easily
Cell differentiation:
● Differentiation is the process by which a cell becomes specialised to be able to perform specific
functions
● Most differentiation occurs as an organism develops.
● In most animal cells, cells differentiate at an early but the ability is lost once the cells become
specialised
● In many plant cells, they are able to differentiate throughout their life
,GCSE Biology: Cell Biology Revision Notes
● In mature animals, cells differentiate mainly to repair and replace cells
● Unspecialised cells develop different subcellular structures to differentiate into different types of
cells to carry out specific functions
Microscopy:
● Light microscopes use light and lenses to form an image of a specimen and magnify it allowing us
to see individual cells and large subcellular structures e.g nuclei
● Electron microscopes use electrons instead of light to form an image and have a higher
magnification and resolution than light microscopes allowing us to see cells in more detail and
smaller subcellular structures e.g ribosomes and mitochondria
● Formula for magnification: magnification = size of image/size of real object
Culturing microorganisms:
● Binary fission: When prokaryotic cells reproduce
○ The circular DNA and plasmids replicate
○ The cell gets bigger and the circular DNA strands move to opposite poles of the cell
○ The cytoplasm begins to divide and new cell walls begin to form
○ The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy
of the circular DNA but a variable number of copies of plasmids
● Bacteria can be grown in nutrient broth solution or solid agar jelly
● They will form visible colonies on the surface of the agar jelly or spread out to give an even coating
of bacteria
● Uncontaminated cultures of microorganisms are required for investigating the action of antibiotics
● Aseptic techniques:
○ The Petri dish and culture medium should be sterilised by heating them at a high
temperature before use to kill any unwanted microorganisms
○ Pass an inoculating loop through a hot flame to sterilise it before transferring the bacteria
to the culture medium
○ Lightly tape the lid of the Petri dish to stop microorganisms from getting in
○ The Petri dish should be stored upside down to stop drops of condensation falling onto the
agar surface
○ Cultures of microorganisms should be kept below 25°C because harmful pathogens are
likely to grow above this temperature
● You can find the area of bacteria colonies by measuring the diameter then using πr²
Chromosomes:
● Chromosomes are coiled up lengths of DNA molecules found in the nucleus
● Each chromosome carries a large number of genes
● Body cells normally have two pairs of chromosomes - one from each parent
● There are 23 pairs of chromosomes in a body cell
Mitosis and cell cycle:
● Body cells divide to produce new cells in a series of stages called the cell cycle
● The stage where the cell divides is called mitosis
● Mitosis is used to grow or replace damaged cells
● The end of of the cell cycle results in two new cells identical to the original cell with the same
number of chromosomes
● Stage 1: Growth and DNA replication
○ Before the cell divides it needs to grow and increase subcellular structures such as
ribosomes and mitochondria
○ It then duplicates DNA so there are two copies of each chromosome
● Stage 2: Mitosis
○ The chromosomes line up at the centre of the cell and cell fibres pull them apart
○ One set of chromosomes is pulled to the opposite ends of the cell
○ Then the nucleus divides into two nuclei
, GCSE Biology: Cell Biology Revision Notes
○ Lastly, the cell membrane and cytoplasm divided
○ The cell has now produced two new daughter cells which are genetically identical to the
parent cell
Stem cells:
● A stem cell is an undifferentiated cell which can divide to produce many more stem cells which can
differentiate into different types of cells
● Stem cells are found in early human embryos and can differentiate into any type of cell
● Stem cells can be found in adults in their bone marrow but these stem cells cannot differentiate
into any type of cell but many cells like blood cells
● Stem cells from embryos and bone marrow can be grown in a lab to produce clones and made to
differentiate into specialised cells for medicine or research
● Medicine already uses adult stem cells to cure diseases
● Embryonic stem cells could be used to replace damaged cells in people
● Therapeutic cloning is where an embryo is made to have the same genetic information as the
patient so the stem cells would have the same genes and wouldn’t be rejected by the patient’s body
● There are risks of using stem cells in medicine like the transfer of viral diseases
● Issues with stem cell research:
○ Some people are against stem cell research because they feel that human embryos are
potential human life
○ Others think curing patients is more important than the rights of embryos
○ They argue that the embryos used are unwanted ones which would have been destroyed
○ Campaigners for the rights of embryos feel scientists should look for other sources of stem
cells
○ In some countries, stem cell research is banned
● In plants, stem cells are found in meristems
● Cells in the meristem tissue can differentiate into any type of plant cell throughout the plant’s
entire life
● These stem cells can be used to produce clones of whole plants quickly and cheaply
● They can be used to grow more plants or rare species
● Stem cells can be used to grow crops of identical plants with desired features
Diffusion:
● Diffusion is the movement of particles from an area of higher concentration to an area of lower
concentration
● Diffusion happens in solutions and gases because the particles are free to move
● The bigger the concentration gradient, the faster the rate of diffusion
● A higher temperature will give a faster diffusion rate because the particles have more energy so
move around faster
● The larger the surface area of the membrane, the faster the rate of diffusion because more particles
can pass through
● Dissolved substances move in and out of a cell through the cell membrane via diffusion
● Only small molecules can diffuse through cell membranes
Osmosis:
● Osmosis is the movement of water molecules from an area of higher water concentration to an
area of lower water concentration through a partially permeable membrane
● Dilute solutions has a higher water concentration than concentrated solutions
● Osmosis is an example of diffusion and is passive transport
Active transport:
● Active transport is the movement of particles from an area of lower concentration to an area of
higher concentration requiring energy from respiration
● Root hair cells take in minerals and water via active transport:
○ The concentration of minerals is higher in the root hair cells than in the soil
Eukaryotes and Prokaryotes:
● All living things are made up of cells which are eukaryotes or prokaryotes
● Eukaryotes: Plant and Animal cells have a cell membrane, cytoplasm and genetic material in a
nucleus
● Prokaryotes: Bacterial cells are much smaller and have cytoplasm and a cell membrane surrounded
by a cell wall and the genetic material is found in a single DNA loop and small DNA rings called
plasmids
Animal and plant cells:
● Animal cells have: nucleus, cytoplasm, cell membrane, mitochondria and ribosomes
● Plant cells have: nucleus, cytoplasm, cell membrane, cell wall, a permanent vacuole, chloroplasts,
mitochondria and ribosomes
● Nucleus - Contains genetic material that controls the activities of the cell
● Cytoplasm - Where chemical reactions take place
● Cell membrane - Controls what enters and leaves the cell. It also holds the cell together.
● Cell wall - Made of cellulose. Supports and strengthens the cell
● Permanent vacuole - Contains cell sap and keeps the cell turgid
● Chloroplasts - Where photosynthesis takes place
● Mitochondria - Where respiration takes place
● Ribosomes - Where protein synthesis takes place
● Plasmids - Small rings of DNA
Cell specialisation:
● Sperm cells: Deliver male DNA to the egg cell where the female DNA is located
○ It has a long tail and streamlined head to help it swim to the egg
○ There are a lot of mitochondria to provide energy for the cell
○ It carries enzymes in its head to digest through the egg membrane
● Nerve cells: Carry electrical impulses from one part of the body to another
○ They have a long axon to carry the impulse over a long distance
○ They have branched connections at both ends to connect to other nerve cells
○ They are insulated in a fatty sheath which helps the impulse move along the nerve quicker
● Muscle cells: Contract quickly for movement
○ They have a lot of mitochondria to provide energy for contraction
○ They have protein filaments which slide over each other for contraction
● Root hair cells: Absorb water and minerals
○ Root hairs increase surface area so the rate of water uptake by osmosis is greater
○ They have thin walls so water can move easily due to a short diffusion distance
○ Mitochondria release energy for active transport of mineral ions
● Xylem cells: Transports water and dissolved minerals
○ The cells are dead and hollow forming hollow tubes which allows water to be drawn
upwards
○ Cells have no organelles to allow water to be drawn upwards
○ Outer walls are strengthened by lignin which thickens it and supports the plant
● Phloem cells: Transports dissolved sugars and amino acids
○ Cells are joined end to end and contain sieve plates with holes to form tubes which allow
amino acids and sugars to flow easily
○ They are living but have few subcellular organisms to allow amino acids and sugars to flow
easily
Cell differentiation:
● Differentiation is the process by which a cell becomes specialised to be able to perform specific
functions
● Most differentiation occurs as an organism develops.
● In most animal cells, cells differentiate at an early but the ability is lost once the cells become
specialised
● In many plant cells, they are able to differentiate throughout their life
,GCSE Biology: Cell Biology Revision Notes
● In mature animals, cells differentiate mainly to repair and replace cells
● Unspecialised cells develop different subcellular structures to differentiate into different types of
cells to carry out specific functions
Microscopy:
● Light microscopes use light and lenses to form an image of a specimen and magnify it allowing us
to see individual cells and large subcellular structures e.g nuclei
● Electron microscopes use electrons instead of light to form an image and have a higher
magnification and resolution than light microscopes allowing us to see cells in more detail and
smaller subcellular structures e.g ribosomes and mitochondria
● Formula for magnification: magnification = size of image/size of real object
Culturing microorganisms:
● Binary fission: When prokaryotic cells reproduce
○ The circular DNA and plasmids replicate
○ The cell gets bigger and the circular DNA strands move to opposite poles of the cell
○ The cytoplasm begins to divide and new cell walls begin to form
○ The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy
of the circular DNA but a variable number of copies of plasmids
● Bacteria can be grown in nutrient broth solution or solid agar jelly
● They will form visible colonies on the surface of the agar jelly or spread out to give an even coating
of bacteria
● Uncontaminated cultures of microorganisms are required for investigating the action of antibiotics
● Aseptic techniques:
○ The Petri dish and culture medium should be sterilised by heating them at a high
temperature before use to kill any unwanted microorganisms
○ Pass an inoculating loop through a hot flame to sterilise it before transferring the bacteria
to the culture medium
○ Lightly tape the lid of the Petri dish to stop microorganisms from getting in
○ The Petri dish should be stored upside down to stop drops of condensation falling onto the
agar surface
○ Cultures of microorganisms should be kept below 25°C because harmful pathogens are
likely to grow above this temperature
● You can find the area of bacteria colonies by measuring the diameter then using πr²
Chromosomes:
● Chromosomes are coiled up lengths of DNA molecules found in the nucleus
● Each chromosome carries a large number of genes
● Body cells normally have two pairs of chromosomes - one from each parent
● There are 23 pairs of chromosomes in a body cell
Mitosis and cell cycle:
● Body cells divide to produce new cells in a series of stages called the cell cycle
● The stage where the cell divides is called mitosis
● Mitosis is used to grow or replace damaged cells
● The end of of the cell cycle results in two new cells identical to the original cell with the same
number of chromosomes
● Stage 1: Growth and DNA replication
○ Before the cell divides it needs to grow and increase subcellular structures such as
ribosomes and mitochondria
○ It then duplicates DNA so there are two copies of each chromosome
● Stage 2: Mitosis
○ The chromosomes line up at the centre of the cell and cell fibres pull them apart
○ One set of chromosomes is pulled to the opposite ends of the cell
○ Then the nucleus divides into two nuclei
, GCSE Biology: Cell Biology Revision Notes
○ Lastly, the cell membrane and cytoplasm divided
○ The cell has now produced two new daughter cells which are genetically identical to the
parent cell
Stem cells:
● A stem cell is an undifferentiated cell which can divide to produce many more stem cells which can
differentiate into different types of cells
● Stem cells are found in early human embryos and can differentiate into any type of cell
● Stem cells can be found in adults in their bone marrow but these stem cells cannot differentiate
into any type of cell but many cells like blood cells
● Stem cells from embryos and bone marrow can be grown in a lab to produce clones and made to
differentiate into specialised cells for medicine or research
● Medicine already uses adult stem cells to cure diseases
● Embryonic stem cells could be used to replace damaged cells in people
● Therapeutic cloning is where an embryo is made to have the same genetic information as the
patient so the stem cells would have the same genes and wouldn’t be rejected by the patient’s body
● There are risks of using stem cells in medicine like the transfer of viral diseases
● Issues with stem cell research:
○ Some people are against stem cell research because they feel that human embryos are
potential human life
○ Others think curing patients is more important than the rights of embryos
○ They argue that the embryos used are unwanted ones which would have been destroyed
○ Campaigners for the rights of embryos feel scientists should look for other sources of stem
cells
○ In some countries, stem cell research is banned
● In plants, stem cells are found in meristems
● Cells in the meristem tissue can differentiate into any type of plant cell throughout the plant’s
entire life
● These stem cells can be used to produce clones of whole plants quickly and cheaply
● They can be used to grow more plants or rare species
● Stem cells can be used to grow crops of identical plants with desired features
Diffusion:
● Diffusion is the movement of particles from an area of higher concentration to an area of lower
concentration
● Diffusion happens in solutions and gases because the particles are free to move
● The bigger the concentration gradient, the faster the rate of diffusion
● A higher temperature will give a faster diffusion rate because the particles have more energy so
move around faster
● The larger the surface area of the membrane, the faster the rate of diffusion because more particles
can pass through
● Dissolved substances move in and out of a cell through the cell membrane via diffusion
● Only small molecules can diffuse through cell membranes
Osmosis:
● Osmosis is the movement of water molecules from an area of higher water concentration to an
area of lower water concentration through a partially permeable membrane
● Dilute solutions has a higher water concentration than concentrated solutions
● Osmosis is an example of diffusion and is passive transport
Active transport:
● Active transport is the movement of particles from an area of lower concentration to an area of
higher concentration requiring energy from respiration
● Root hair cells take in minerals and water via active transport:
○ The concentration of minerals is higher in the root hair cells than in the soil
