AQA GCSE Biology (8461) — Cell Biology
You can easily squish a caterpillar, but try squishing a sturdy oak tree. The differences in how these organisms look and feel come down to the microscopic structures hidden inside their cells.
Both plant and animal cells are classified as eukaryotic cells, meaning their genetic material is enclosed within a nucleus. Most types of animal cells differentiate at an early stage of development to become specialised for specific jobs.
An animal cell contains five primary sub-cellular structures:
A plant cell contains the exact same five structures as an animal cell, but has three additional components that animal cells lack. These are:
Algal cells are also eukaryotic and share a very similar structure to plant cells, notably possessing a cell wall made of cellulose.
Every structure inside a cell has a specific mechanism that supports the cell's life and survival.
Bacteria are prokaryotic cells. They are much smaller than eukaryotic cells and fundamentally differ because they lack a nucleus. Instead, their genetic material is found as a single, large loop of DNA free within the cytoplasm.
Prokaryotic cells may also contain plasmids. These are small, circular rings of DNA that are separate from the main bacterial chromosome.
The cell wall in plant and algal cells is located outside the cell membrane. It is primarily made of cellulose, a tough, complex carbohydrate.
When a plant cell absorbs water via osmosis, it faces a physical problem: the internal pressure increases. The turgor mechanism solves this:
Crucially, the cellulose cell wall prevents lysis (bursting). If an animal cell is placed in a dilute solution, it will take in water and burst because it lacks this rigid outer layer.
Never refer to the nucleus as the 'brain of the cell'. Mark schemes explicitly reject this; you must state that it 'controls the activities of the cell' or 'contains genetic material'.
Do not say that mitochondria 'make' or 'produce' energy. The strict AQA requirement is that they 'release' or 'transfer' energy during aerobic respiration.
When explaining how a cell wall works, explicitly link the chemical 'cellulose' to the physical result 'prevents bursting'. Do not say the cell membrane prevents bursting.
If an exam question asks you to compare an animal cell to a plant cell, explicitly state the negative features (e.g., 'animal cells DO NOT have a cell wall or permanent vacuole').
When defining plasmids, ensure you use the exact phrasing 'small rings of DNA' or 'loops of DNA' to secure the mark.
Eukaryotic cells
Cells that contain a nucleus and membrane-bound organelles, such as animal, plant, and algal cells.
Prokaryotic cells
Smaller, simpler cells (such as bacteria) that lack a nucleus and have their genetic material as a single DNA loop.
Nucleus
Contains genetic material (DNA/chromosomes) which controls the activities of the cell.
Cytoplasm
A gel-like substance where most of the cell's chemical reactions happen, containing enzymes to control them.
Cell membrane
A partially permeable barrier that controls the movement of substances into and out of the cell.
Mitochondria
The site of aerobic respiration, where energy is released for the cell to use.
Ribosomes
The site where protein synthesis takes place.
Chloroplasts
Organelles found in plant and algal cells that are the site of photosynthesis.
Permanent vacuole
A large sac in the cytoplasm of plant cells filled with cell sap, which maintains the cell's turgidity to provide support.
Cell wall
A rigid structure located outside the cell membrane in plant, algal, and bacterial cells that strengthens the cell.
Cellulose
A tough carbohydrate that is the main component of plant and algal cell walls, providing structural rigidity.
Chlorophyll
The green pigment inside chloroplasts that absorbs the light energy required for photosynthesis.
Plasmids
Small, circular loops of DNA found in the cytoplasm of prokaryotic cells that can carry advantageous extra genes.
Vector
A mechanism, such as a plasmid, used to transport genetic material into a cell during genetic engineering.
Turgid
The firm state of a plant cell when it is swollen with water, pushing the cell membrane hard against the cell wall.
Lysis
The bursting of a cell, which occurs in animal cells when they take in too much water, but is prevented in plant cells by the cell wall.
Aerobic respiration
The process occurring in mitochondria where energy is released for the cell to use.
Protein synthesis
The process of making proteins, which takes place at the ribosomes.
Cell sap
A dilute solution of mineral salts, sugars, and organic acids found inside the permanent vacuole.
Put your knowledge into practice — try past paper questions for Biology
Eukaryotic cells
Cells that contain a nucleus and membrane-bound organelles, such as animal, plant, and algal cells.
Prokaryotic cells
Smaller, simpler cells (such as bacteria) that lack a nucleus and have their genetic material as a single DNA loop.
Nucleus
Contains genetic material (DNA/chromosomes) which controls the activities of the cell.
Cytoplasm
A gel-like substance where most of the cell's chemical reactions happen, containing enzymes to control them.
Cell membrane
A partially permeable barrier that controls the movement of substances into and out of the cell.
Mitochondria
The site of aerobic respiration, where energy is released for the cell to use.
Ribosomes
The site where protein synthesis takes place.
Chloroplasts
Organelles found in plant and algal cells that are the site of photosynthesis.
Permanent vacuole
A large sac in the cytoplasm of plant cells filled with cell sap, which maintains the cell's turgidity to provide support.
Cell wall
A rigid structure located outside the cell membrane in plant, algal, and bacterial cells that strengthens the cell.
Cellulose
A tough carbohydrate that is the main component of plant and algal cell walls, providing structural rigidity.
Chlorophyll
The green pigment inside chloroplasts that absorbs the light energy required for photosynthesis.
Plasmids
Small, circular loops of DNA found in the cytoplasm of prokaryotic cells that can carry advantageous extra genes.
Vector
A mechanism, such as a plasmid, used to transport genetic material into a cell during genetic engineering.
Turgid
The firm state of a plant cell when it is swollen with water, pushing the cell membrane hard against the cell wall.
Lysis
The bursting of a cell, which occurs in animal cells when they take in too much water, but is prevented in plant cells by the cell wall.
Aerobic respiration
The process occurring in mitochondria where energy is released for the cell to use.
Protein synthesis
The process of making proteins, which takes place at the ribosomes.
Cell sap
A dilute solution of mineral salts, sugars, and organic acids found inside the permanent vacuole.
