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AQA GCSE Biology paper 1 summary notes
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Summary notes for AQA biology paper 1 (Year 10 content). Includes labelled diagrams and exam style explanations.
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CELL BIOLOGYCELL STRUCTURE
Eukaryotes and prokaryotes
Eukaryotic cells Prokaryotic cells
Plant, animal cells Bacterial cells
Cell membrane, cytoplasm, Cell membrane, cytoplasm,
nucleus cell wall
Genetic material enclosed in a Genetic material not enclosed
nucleus in a nucleus
- single DNA loop, sometimes RP 1: Microscopy
small rings of DNA called
plasmids Aim
- Use a light microscope to investigate a selection of plant and
animal cells
Equipment
- Light microscope
- Slide
- Cover slip
- Onion
- Forceps
- Iodine solution
- White tile
Method
1. Peel off an epidermal layer on the onion
Example of a bacterial cell
2. Add a drop of water on a slide and place the tissue
3. Add a drop of iodine solution to stain the cells, for easy
observation
Animal and plant cells 4. Place the cover slip and make sure no air bubbles are
trapped
5. Place the slide on the microscope
• Animal cells 6. Select the lowest power objective lens
Cell membrane = controls what goes in and out of the cell 7. Turn the coarse focussing dial so the slide just touches the
Ribosomes = site of protein synthesis objective lens
Mitochondria = site of aerobic respiration 8. While looking into the eyepiece, turn the coarse focussing
Cytoplasm = most of the chemical reactions take place dial to move the stage away, until the image comes into
Nucleus = controls all the activities of the cell focus
9. Repeat with a higher power objective lens
Cell differentiation
• Cell differentiation = the process by which a cell changes to
become specialised
- Animal cells:
The cells differentiate at an early stage
In mature animals, cell division is mainly used for
repairing and replacing cells like skin or blood cells
- Plant cells:
Plant cells retain the ability to differentiate throughout life
• Plant cells
Cellulose cell wall = strengthens the cell and gives support
Permanent vacuole = filled with cell sap and keeps the cell rigid
Chloroplast = contain chlorophyll which absorbs light needed
for photosynthesis
Cell specialisation
, - The cells die and form hollow tubes so that water can move
easily
• Nerve cells [carry electrical impulses] - Spirals of lignin which supports the cell and the plant stem
from the pressure of water moving up the plant
-
• Phloem cells [carry nutrients]
- Lots of dendrites to make connections to other nerve cells
- Long axon to carry the nerve impulse around the body
• Muscle cells [contract and relax]
- Lots of mitochondria to release energy needed
- Sieve plates made from cell walls which help to transport
- Store glycogen which can be broken down and used for
and absorb the nutrients
respiration
- Companion cells to transfer energy and keep phloem cells
alive
• Sperm cells [fertilise]
Microscopy
• Electron microscope
- Higher magnification, higher resolution than light
microscope, but object needs to be in vacuum
- Can be used to study cells in finer detail
• Calculations
- Long tail for swimming
- Many mitochondria in the middle section to release energy
- Enzyme in acrosome to break the eggshell
- Large nucleus which contains genetic information
• Root hair cells [take up water and mineral ions] • Orders of magnitude
- 10x bigger (10^1) = 1 order of magnitude bigger
- 100x bigger (10^2) = 2 orders of magnitude bigger
• Relative sizes
- Large surface area for water to move in
- Large permanent vacuole to keep the concentration gradient
for osmosis
- Many mitochondria to release energy needed for active
transport of mineral ions
• Xylem cells [carry water and mineral ions]
Culturing microorganisms
Bacteria multiply by binary fission (simple cell division) as often as
once every 20 minutes If they are in a suitable condition
Bacteria can be grown in a nutrient broth solution or on an agar gel
plate as colonies
• Preparing uncontaminated culture (aseptic techniques)
Sterilising Petri dishes and culture media
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