Biology A Level Revision (AQA)
Paper 1 - Year 12 / AS Level
Biological Molecules
Cells
Organisms Exchanging Substances
Genetic Information, Variation
Paper 2 - Year 13 / A Level
Energy Transfers In and Between Organisms
Organisms Responses to their Environment
Genetics, Evolution and Ecosystems
The Control of Gene Expression
Some diagrams used in this document are sourced from Cognito (https://cognitoedu.org).
All rights to those diagrams belong to Cognito.
, Biology Revision A Level AQA
Cells
Introduction to Cells
● Eukaryotic VS Prokaryotic
- All life exists as cells which are the smallest unit of a living thing. All cells are grouped
into eukaryotic and prokaryotic cells.
- Similarities:
➢ Both cells contain organelles .
➢ Both cell-surface membranes are made up of a phospholipid bilayer.
- Differences:
➢ Prokaryotic cells are made up of single-celled organisms (bacteria) while
eukaryotic cells make up complex organisms (animals / plants).
➢ Eukaryotic cells are larger and more complex than prokaryotic cells.
➢ Cells divide by binary fission in prokaryotic cells but in eukaryotic cells, they
divide by mitosis / meiosis.
● Types of Eukaryotic cells
- Animal cells are made up of many organelles like:
➢ Nucleus, mitochondria, cell membrane, ribosomes, cytoplasm, endoplasmic
reticulum, lysosomes and a golgi apparatus with golgi vesicles.
- Plant cells are made up of everything an animal cell has but also have:
➢ Vacuole, chloroplasts and a cell wall.
- Algal cells (identical organelles to plant cells).
- Fungal cells (similar to plants but do not have chloroplasts and their cell walls are
made up of chitin).
● Specialisation
- Cells gain specific roles in complex organisms and are grouped to perform this.
- A cell specialises because the contents / shape aid a specific function.
➢ Muscle cells have lots of mitochondria to produce lots of ATP as they are active.
➢ RBC are biconcave shaped and have no nucleus to maximise space to carry oxygen.
➢ Palisade cells are packed with chloroplasts to absorb light for photosynthesis.
- Specialised cells are grouped into tissues.
- Tissues are grouped into organs.
- Organs are grouped into organ systems.
Page 1
, Biology Revision A Level AQA
Eukaryotic Organelles
● Plasma Membrane
- Structure - Made up of a phospholipid bilayer and have proteins
/ cholesterol embedded in them. These act as receptors.
- Function - Controls the passage of substances in and out of the
cell. Waste products leave by passing through the plasma
membrane.
● Cytoplasm
- Structure - Made up of organelles suspended in the gel-like cytosol. Water makes up
70% of the cytoplasm and contains proteins, sugars, ions and fatty acids.
- Function - Most metabolic reactions take place here and many different organelles
(which are parts of a cell) perform specific functions within the cytoplasm.
● Nucleus
- Structure - The nucleus is full of a fluid called nucleoplasm
which has chromatin and the nucleolus. Eukaryotes have
linear chromosomes that are made up of DNA. A nuclear
envelope surrounds the structure and acts as a
double-membrane. The nuclear envelope has pores which
control the passage of ions, RNA and molecules between the
nucleoplasm and cytoplasm.
- Function - The cell is controlled by the nucleus. DNA within the
nucleus contains instructions for protein synthesis.
● Ribosome
- Structure - Ribosomes float freely in the cytoplasm or are attached to
the RER. These organelles are very small made up of protein subunits
and are not covered with a membrane.
- Function - Ribosomes are the site of protein synthesis which is
essential in every cell.
● Endoplasmic Reticulum (ER)
- Structure - Made up of interconnected membranous sacs and
tubules. They have a phospholipid bilayer to act as their membrane. The
rough ER has ribosomes on its surface while the smooth ER does not.
- Function - The rough ER is responsible for processing and folding
proteins. The smooth ER is responsible for making and processing lipids.
● Lysosomes
- Structure - Are a type of golgi vesicle that contain
hydrolytic enzymes called lysozymes.
- Function - Lysozymes digest pathogens and break
down waste materials.
Page 2
Paper 1 - Year 12 / AS Level
Biological Molecules
Cells
Organisms Exchanging Substances
Genetic Information, Variation
Paper 2 - Year 13 / A Level
Energy Transfers In and Between Organisms
Organisms Responses to their Environment
Genetics, Evolution and Ecosystems
The Control of Gene Expression
Some diagrams used in this document are sourced from Cognito (https://cognitoedu.org).
All rights to those diagrams belong to Cognito.
, Biology Revision A Level AQA
Cells
Introduction to Cells
● Eukaryotic VS Prokaryotic
- All life exists as cells which are the smallest unit of a living thing. All cells are grouped
into eukaryotic and prokaryotic cells.
- Similarities:
➢ Both cells contain organelles .
➢ Both cell-surface membranes are made up of a phospholipid bilayer.
- Differences:
➢ Prokaryotic cells are made up of single-celled organisms (bacteria) while
eukaryotic cells make up complex organisms (animals / plants).
➢ Eukaryotic cells are larger and more complex than prokaryotic cells.
➢ Cells divide by binary fission in prokaryotic cells but in eukaryotic cells, they
divide by mitosis / meiosis.
● Types of Eukaryotic cells
- Animal cells are made up of many organelles like:
➢ Nucleus, mitochondria, cell membrane, ribosomes, cytoplasm, endoplasmic
reticulum, lysosomes and a golgi apparatus with golgi vesicles.
- Plant cells are made up of everything an animal cell has but also have:
➢ Vacuole, chloroplasts and a cell wall.
- Algal cells (identical organelles to plant cells).
- Fungal cells (similar to plants but do not have chloroplasts and their cell walls are
made up of chitin).
● Specialisation
- Cells gain specific roles in complex organisms and are grouped to perform this.
- A cell specialises because the contents / shape aid a specific function.
➢ Muscle cells have lots of mitochondria to produce lots of ATP as they are active.
➢ RBC are biconcave shaped and have no nucleus to maximise space to carry oxygen.
➢ Palisade cells are packed with chloroplasts to absorb light for photosynthesis.
- Specialised cells are grouped into tissues.
- Tissues are grouped into organs.
- Organs are grouped into organ systems.
Page 1
, Biology Revision A Level AQA
Eukaryotic Organelles
● Plasma Membrane
- Structure - Made up of a phospholipid bilayer and have proteins
/ cholesterol embedded in them. These act as receptors.
- Function - Controls the passage of substances in and out of the
cell. Waste products leave by passing through the plasma
membrane.
● Cytoplasm
- Structure - Made up of organelles suspended in the gel-like cytosol. Water makes up
70% of the cytoplasm and contains proteins, sugars, ions and fatty acids.
- Function - Most metabolic reactions take place here and many different organelles
(which are parts of a cell) perform specific functions within the cytoplasm.
● Nucleus
- Structure - The nucleus is full of a fluid called nucleoplasm
which has chromatin and the nucleolus. Eukaryotes have
linear chromosomes that are made up of DNA. A nuclear
envelope surrounds the structure and acts as a
double-membrane. The nuclear envelope has pores which
control the passage of ions, RNA and molecules between the
nucleoplasm and cytoplasm.
- Function - The cell is controlled by the nucleus. DNA within the
nucleus contains instructions for protein synthesis.
● Ribosome
- Structure - Ribosomes float freely in the cytoplasm or are attached to
the RER. These organelles are very small made up of protein subunits
and are not covered with a membrane.
- Function - Ribosomes are the site of protein synthesis which is
essential in every cell.
● Endoplasmic Reticulum (ER)
- Structure - Made up of interconnected membranous sacs and
tubules. They have a phospholipid bilayer to act as their membrane. The
rough ER has ribosomes on its surface while the smooth ER does not.
- Function - The rough ER is responsible for processing and folding
proteins. The smooth ER is responsible for making and processing lipids.
● Lysosomes
- Structure - Are a type of golgi vesicle that contain
hydrolytic enzymes called lysozymes.
- Function - Lysozymes digest pathogens and break
down waste materials.
Page 2
