AQA A level Biology - topic 2 Cells
This content is for Year 1/AS Level and is one of
the first topics you will learn and need to know.
All subtopics are underlined
This topic is called Cells
Cells
Eukaryotic Cells
Eukaryotic cells are more complex than prokaryotic cells because they
have membrane-bound organelles, including a nucleus. We can separate
it into animal and plant eukaryotic cells, highlighting the key structures
and their functions.
1. Nucleus
Structure: Surrounded by a double membrane called the nuclear
envelope with pores; contains chromatin (DNA + proteins) and
sometimes a nucleolus.
Function:
o Stores genetic information (DNA) which controls the cell’s
activities.
o Nucleolus makes ribosomes.
o Nuclear pores allow transport of mRNA and ribosomal
subunits.
2. Mitochondria
Structure: Double membrane; inner membrane folded into cristae;
internal space called the matrix.
Function:
o Site of aerobic respiration, producing ATP.
, o Self-replicating and contains its own DNA.
3. Ribosomes
Structure: Small (80S in eukaryotes); not membrane-bound.
Function: Protein synthesis.
4. Endoplasmic Reticulum (ER)
Rough ER: Studded with ribosomes; synthesizes proteins for
secretion or membranes.
Smooth ER: No ribosomes; synthesizes lipids and steroids, and
detoxifies substances.
5. Golgi Apparatus
Structure: Stacks of flattened membranes (cisternae).
Function:
o Modifies and packages proteins and lipids.
o Forms lysosomes.
6. Lysosomes
(more prominent in animal cells)
Structure: Membrane-bound vesicles containing hydrolytic enzymes.
Function:
o Digests worn-out organelles and pathogens (cellular waste
management).
7. Cytoskeleton
Structure: Network of microfilaments, microtubules, and
intermediate filaments.
Function:
o Maintains cell shape.
o Supports movement of organelles.
o Forms spindle fibers in cell division.
, 8. Cell Membrane
Structure: Phospholipid bilayer with proteins, cholesterol, and
carbohydrates.
Function:
o Controls movement of substances in and out.
o Involved in cell communication and signaling.
Plant Cell Specific Structures
9. Cell Wall
Structure: Made of cellulose.
Function: Provides support and structure; protects against osmotic
pressure.
10. Vacuole
Structure: Large, permanent vacuole filled with cell sap.
Function:
o Maintains turgor pressure.
o Stores water, ions, and other molecules.
11. Chloroplasts
Structure: Double membrane; internal stacks of thylakoids called
grana, connected by stroma lamellae; contains stroma with
enzymes and DNA.
Function: Site of photosynthesis, producing glucose.
Key Differences Between Plant and Animal Eukaryotic
Cells
Feature Plant Cell Animal Cell
Cell wall Present Absent
Chloropla Present Absent
This content is for Year 1/AS Level and is one of
the first topics you will learn and need to know.
All subtopics are underlined
This topic is called Cells
Cells
Eukaryotic Cells
Eukaryotic cells are more complex than prokaryotic cells because they
have membrane-bound organelles, including a nucleus. We can separate
it into animal and plant eukaryotic cells, highlighting the key structures
and their functions.
1. Nucleus
Structure: Surrounded by a double membrane called the nuclear
envelope with pores; contains chromatin (DNA + proteins) and
sometimes a nucleolus.
Function:
o Stores genetic information (DNA) which controls the cell’s
activities.
o Nucleolus makes ribosomes.
o Nuclear pores allow transport of mRNA and ribosomal
subunits.
2. Mitochondria
Structure: Double membrane; inner membrane folded into cristae;
internal space called the matrix.
Function:
o Site of aerobic respiration, producing ATP.
, o Self-replicating and contains its own DNA.
3. Ribosomes
Structure: Small (80S in eukaryotes); not membrane-bound.
Function: Protein synthesis.
4. Endoplasmic Reticulum (ER)
Rough ER: Studded with ribosomes; synthesizes proteins for
secretion or membranes.
Smooth ER: No ribosomes; synthesizes lipids and steroids, and
detoxifies substances.
5. Golgi Apparatus
Structure: Stacks of flattened membranes (cisternae).
Function:
o Modifies and packages proteins and lipids.
o Forms lysosomes.
6. Lysosomes
(more prominent in animal cells)
Structure: Membrane-bound vesicles containing hydrolytic enzymes.
Function:
o Digests worn-out organelles and pathogens (cellular waste
management).
7. Cytoskeleton
Structure: Network of microfilaments, microtubules, and
intermediate filaments.
Function:
o Maintains cell shape.
o Supports movement of organelles.
o Forms spindle fibers in cell division.
, 8. Cell Membrane
Structure: Phospholipid bilayer with proteins, cholesterol, and
carbohydrates.
Function:
o Controls movement of substances in and out.
o Involved in cell communication and signaling.
Plant Cell Specific Structures
9. Cell Wall
Structure: Made of cellulose.
Function: Provides support and structure; protects against osmotic
pressure.
10. Vacuole
Structure: Large, permanent vacuole filled with cell sap.
Function:
o Maintains turgor pressure.
o Stores water, ions, and other molecules.
11. Chloroplasts
Structure: Double membrane; internal stacks of thylakoids called
grana, connected by stroma lamellae; contains stroma with
enzymes and DNA.
Function: Site of photosynthesis, producing glucose.
Key Differences Between Plant and Animal Eukaryotic
Cells
Feature Plant Cell Animal Cell
Cell wall Present Absent
Chloropla Present Absent
