Topic 2 Cells model answer revision notes AQA A Level Biology

AQA A Level Biology


Topic 2 Cells
Model answer notes by @biologywitholivia (updated for 2025)




Topic Understand Memorise Practise


2.1.1 Structure of eukaryotic cells


2.1.2 Structure of prokaryotic cells and of viruses


2.1.3 Methods of studying cells


2.2 All cells arise from other cells


Required practical 2


2.3 Transport across cell membranes


Required practical 3


Required practical 4


2.4 Cell recognition and the immune system




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2.1 Cell structure
2.1.1 Structure of eukaryotic cells
What are the distinguishing features of eukaryotic cells?

●​ Cytoplasm containing membrane-bound organelles
●​ So DNA enclosed in a nucleus



Describe the general structure of eukaryotic cells




Algal and fungal cells are similar to plant cells - see differences above.


Describe the structure of the cell-surface membrane




More detail covered in 2.3 Transport across cell membranes.


Describe the function of the cell-surface membrane

●​ Selectively permeable → enables control of passage of substances in / out of cell
●​ Molecules / receptors / antigens on surface → allow cell recognition / signalling




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Describe the structure of the nucleus




Describe the function of the nucleus

●​ Holds / stores genetic information which codes for polypeptides (proteins)
●​ Site of DNA replication
●​ Site of transcription (part of protein synthesis), producing mRNA
●​ Nucleolus makes ribosomes / rRNA



Describe the structure of a ribosome
●​ Made of ribosomal RNA and protein (two subunits)
●​ Not a membrane-bound organelle


Describe the function of a ribosome

Site of protein synthesis (translation)



Describe the structure of rough (rER) & smooth endoplasmic reticulum (sER)




Describe the function of rER and sER

rER ●​ Ribosomes on surface synthesise proteins
●​ Proteins processed / folded / transported inside rER
●​ Proteins packaged into vesicles for transport eg. to Golgi apparatus

sER ●​ Synthesises, processes, transports and packages lipids & carbohydrates
●​ Eg. cholesterol and steroid hormones




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Describe the structure of Golgi apparatus and Golgi vesicles




Describe the function of Golgi apparatus and Golgi vesicles

Golgi ●​ Modifies protein, eg. adds carbohydrates to produce glycoproteins
apparatus ●​ Modifies lipids, eg. adds carbohydrates to make glycolipids
●​ Packages proteins / lipids into Golgi vesicles
●​ Produces lysosomes (a type of Golgi vesicle)

Golgi ●​ Transports proteins / lipids to their required destination
vesicles ●​ Eg. moves to and fuses with cell-surface membrane



Describe the structure of lysosomes




Describe the function of lysosomes

●​ Release hydrolytic enzymes (eg. lysozymes)
●​ To break down / hydrolyse pathogens or worn-out cell components



Describe the structure of mitochondria




Describe the function of mitochondria

●​ Site of aerobic respiration
●​ To produce ATP for energy release (from respiratory substrates)
●​ Eg. for protein synthesis / vesicle movement / active transport



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