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AQA A-Level Biology. 3.2 - Cells. May 2024 Exam Review
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AQA A-Level Biology. 3.2 - Cells. May 2024 Exam Review
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AQA A-Level Biology. 3.2 - Cells. May2024 Exam Review
Structure of Nucleus. - Answer>> 1. Nuclear envelope: double
membrane surrounding nucleus, outer membrane continuous with
the (R)ER of the cell.
2. Nuclear pores: allow the passage of larger molecules, such as
mRNA, out of the nucleus.
3. Nucleoplasm: granular, jelly-like material making up the bulk of
the nucleus.
4. Chromosomes: protein-bound, linear DNA.
5. Nucleolus: small spherical region(s) in nucleoplasm.
Manufactures ribosomal RNA and assembles ribosomes.
Function of Nucleus. - Answer>> 1. Controls cell's activities -
produces mRNA and tRNA - protein synthesis. Controls entry and
exit of materials, and contains nuclear reactions.
2. Retains genetic material in the form of DNA and chromosomes.
3. Manufactures ribosomal RNA and ribosomes.
Structure of Mitochondria. - Answer>> 1. Double membrane
surrounding organelle - controls entry and exit of material.
2. Cristae - extensions of the inner membrane, providing a large
surface area for the attachment of enzymes and other proteins
during respiration.
,3. Matrix - makes up the remainder - contains proteins, lipids,
ribosomes and DNA (allows mitochondria to produce own
proteins) and some respiratory enzymes.
Functions of Mitochondria. - Answer>> 1. Sites of Krebs Cycle
and oxidative phosphorylation pathway in aerobic respiration -
responsible for ATP production.
NB = found in high numbers in metabolically active cells which
require much ATP.
Structure of Chloroplasts. - Answer>> Found in plants and
algae.
1. Chloroplast envelope - double plasma membrane, highly
selective, surrounds the organelle.
2. Grana - stacks of disc-shaped thylakoid membrane.
3. Thylakoids - contain chlorophyll used in photosynthesis, can be
linked by lamellae to other grana.
4. Stroma - fluid-filled matrix where Calvin Cycle takes place. Also
contains starch grains.
Functions of Chloroplasts. - Answer>> Site of Photosynthesis:
LDR in thylakoid membranes.
LIR in stroma.
1. Granal membranes provide a large SA for LDR - photosystems,
e- carriers and enzymes etc.
,2. Chloroplasts contain DNA and ribosomes - can quickly and
easily manufacture some of the proteins needed for
photosynthesis.
Structure of Endoplasmic Reticulum. - Answer>> 1. 3D system
of sheet-like membranes - continuous with the outer membrane of
the nuclear double membrane.
2. Membrane contains a network of tubules and flattened sacs
called cisternae.
3. RER - ribosomes on the outer surface of the membranes.
4. SER - lacks ribosomes on its surface and is often more tubular
in its appearance.
Function of Endoplasmic Reticulum. - Answer>> RER
1. Large SA for protein/glycoprotein synthesis.
2. Provides a pathway for material transport throughout the cell,
especially for proteins.
SER
1. Synthesises, stores and transports lipids and carbohydrates.
NB = cells that manufacture and store lots of lipids, carbs and
proteins have extensive ER - such as liver and secretory cells,
such as the intestine epithelial cells.
Structure of Golgi Apparatus. - Answer>> 1. Compact system of
flattened sacs and stacked membranes (cisternae).
, 2. Vesicles - modified proteins and lipids transported to cell
membrane where they fuse with it, and then egest contents to the
outside.
Functions of Golgi Apparatus. - Answer>> 1. Form
glycoproteins by adding carbs to proteins.
2. Produce secretory enzymes, such as those secreted by the
pancreas - apparatus is developed in secretory cells, especially
those in the small intestine.
3. Secrete carbs, such as cellulose for plant cell walls.
4. Transports, modifies and stores lipids.
5. Forms lysosomes.
NB = Golgi Vesicles are 'pinched off' from golgi cisternae.
Structure of Lysosomes. - Answer>> Golgi vesicles with
proteases, lipase and lysozymes.
Functions of Lysosomes. - Answer>> 1. Hydrolyse foreign
material ingested by phagocytes.
2. Exocytosis of enzymes to destroy extra-cellular material.
3. Apoptosis - programmed cell death.
Autolysis - breaking down cells after death.
4. Digest worn out organelles - can recycle chemicals.
NB = very abundant in secretory cells and phagocytes.
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