Eukaryotic and prokaryotic cells, subcellular structures, specialised cells and microscopy. Covers the cell structure section of AQA GCSE Biology Topic 1.
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1.What are the two main types of cell?
Eukaryotic and prokaryotic.
2.What is a eukaryotic cell?
A cell where the genetic material is enclosed in a nucleus. Animal, plant and fungal cells are eukaryotic.
3.What is a prokaryotic cell?
A cell with no nucleus. Its genetic material is a single loop of DNA free in the cytoplasm. Bacteria are prokaryotic.
4.Which is larger, a prokaryotic or a eukaryotic cell?
Eukaryotic cells are much larger. Prokaryotic cells are typically a hundredth of the volume.
5.Name five subcellular structures found in an animal cell.
Nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
6.What is the function of the nucleus?
It contains the genetic material (DNA) that controls the activities of the cell.
7.What is the function of the cytoplasm?
A jelly-like substance where most of the chemical reactions of the cell happen. It contains the enzymes that control those reactions.
8.What is the function of the cell membrane?
It controls which substances enter and leave the cell.
9.What is the function of mitochondria?
They are where aerobic respiration takes place, releasing energy for the cell.
10.What is the function of ribosomes?
They are where protein synthesis happens.
11.Which three structures does a plant cell have that an animal cell does not?
A cell wall, a permanent vacuole and chloroplasts.
12.What is the plant cell wall made of and what does it do?
Cellulose. It strengthens the cell and helps it keep its shape.
13.What is the function of chloroplasts?
They contain chlorophyll, absorb light and are where photosynthesis takes place.
14.What is the function of the permanent vacuole?
It contains cell sap and helps keep the cell rigid by pressing outwards on the cell wall.
15.Which structures are found in a bacterial cell?
Cell wall, cell membrane, cytoplasm, a single loop of DNA and often plasmids. There is no nucleus, no mitochondria and no chloroplasts.
16.What is a plasmid?
A small ring of extra DNA found in bacterial cells, separate from the main loop of DNA.
17.What is cell differentiation?
The process by which a cell changes to become specialised for a particular job.
18.When do most animal cells differentiate?
At an early stage of development. Most animal cells lose the ability to differentiate as they mature, keeping only the ability to repair and replace.
19.How is this different in plants?
Many plant cells keep the ability to differentiate throughout the life of the plant.
20.How is a sperm cell adapted to its function?
It has a tail to swim to the egg, many mitochondria to release energy for swimming, and enzymes in the head to digest through the membrane of the egg.
21.How is a nerve cell adapted to its function?
It has a long axon to carry electrical impulses a long way, branched endings to connect to other neurones, and a myelin sheath to speed up transmission.
22.How is a muscle cell adapted to its function?
It contains protein fibres that can contract to make the cell shorter, and many mitochondria to release the energy needed.
23.How is a root hair cell adapted to its function?
A long hair-like extension gives a large surface area for absorbing water and mineral ions, and many mitochondria supply energy for active transport. It has no chloroplasts.
24.How are xylem cells adapted to their function?
They are hollow dead cells with no end walls, forming a continuous tube, and are strengthened by lignin. They carry water and mineral ions up the plant.
25.How are phloem cells adapted to their function?
Cells are joined end to end with sieve plates between them and have few subcellular structures, so dissolved sugars can flow through. Companion cells provide the energy.
26.State the magnification formula.
magnification = size of image divided by size of real object
27.How do you rearrange the magnification formula to find real size?
real size = size of image divided by magnification
28.What is resolution?
The ability to distinguish between two separate points. Higher resolution means more detail can be seen.
29.Give two advantages of an electron microscope over a light microscope.
It has much higher magnification and much higher resolution, so smaller subcellular structures such as ribosomes and the internal structure of mitochondria can be seen.
30.Why has the electron microscope been important in biology?
Its greater magnification and resolution let scientists see subcellular structures in detail, which increased our understanding of how cells work.
31.How many micrometres are there in a millimetre?
1 mm = 1000 micrometres.
32.How many nanometres are there in a micrometre?
1 micrometre = 1000 nanometres.
33.Convert 0.0025 mm into micrometres.
2.5 micrometres. Multiply by 1000.
34.Why are cells usually stained before being viewed under a light microscope?
Most cells are transparent, so a stain increases contrast and makes the structures visible.
35.An image of a cell is 50 mm wide and the real cell is 0.05 mm wide. What is the magnification?
Magnification = 50 divided by 0.05 = x1000.
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