1
Q
What are eukaryotic cells?
A
- Contain the genetic information in the nucleus
- Complex cells and are all plant and animal cells.
- 10-100 micrometres
2
Q
What are prokaryotic cells?
A
- No nucleus
- Genetic information floats in the cytoplasm.
- Single-celled organisms
- 1-10 micrometres
3
Q
What sub-cellular structures do all eukaryotic cells have?
A
- Cytoplasm - jelly-like substance where all chemical reactions occur.
- Mitochondria - where cellular respiration occurs. Contains the enzymes for it.
- Cell membrane - has a selective barrier which controls what enters and leaves the cell.
4
Q
What do plant cells have that animal cells don’t?
A
- Chloroplast - contain green chlorophyll that help with photosynthesis. (Green parts of plant).
- Cell wall - surrounds cell, made of cellulose to support the cell.
- Vacuole - contains cell sap (keeps the cell rigid and plant upright)
5
Q
What sub-cellular structures do all prokaryotic cells have?
A
- Cell wall
- Genetic material floating freely
- Cell membrane
- Pili - hairlike structures that help cells attach to structures.
- Plasmid - circular loops of DNA that hold extra genes and help in times of stress, where antibiotic resistant bacteria are found.
6
Q
Total magnification equation and magnification equation
A
total magnification = eyepiece lens magnification x objective lens magnification
magnification = image size/real size
7
Q
Why and how are cells stained before observed?
A
- Cells are usually colourless, they are stained to make it easy to observe
- Place cell on a glass slide, add some stain, place the coverslip on top and clear bubbles.
8
Q
What is an electron microscope?
A
- They use electrons as opposed to light to produce an image.
- They give a greater resolution (smallest distance between two points that can be seen as separate entities) than light microscopes
9
Q
What are the two types of electron microscope?
A
TEM: - Produce the most magnified image
- Beam of electrons pass through a thin slice of sample
SEM: - 3D image
- Beam of electrons sent across the surface of a specimen, reflected electrons produce an image.
10
Q
Advantages and disadvantages of light microscopes.
A
- Cheap and easy to use
- Small
- Simple to prepare a sample
- Specimens can living or dead
- Resolution up to 2 X 10^-7 m
11
Q
Advantages and disadvantages of electrons microscopes.
A
- Expensive to buy and use
- Large and difficult to move
- Sample preparation is complex
- False colour added as images are black and white
- Dead specimens
- Resolution is 1 X 10^-10 m
12
Q
What is DNA?
A
Biological polymer with double helixical structure made from nucleotide monomers. They contain all the genetic material and instructions needed for new organism formation.
13
Q
What is the structure of DNA?
A
- A long molecule of coiled up DNA is called a chromosome
- 46 chromosomes in humans
- A short section of DNA is called a gene.
- Made up of 2 strands joined together by bases.
14
Q
What small units are DNA made up of?
A
- DNA is made up of nucleotides which are joined up to make it a polymer of nucleotide monomers
DNA nucleotide has a phosphate, sugar and base - 4 types of nucleotide bases, Adenine, Thymine, Cytosine and Guanine.
A-T C-G
15
Q
How is a copy of DNA made? (Transcription)
A
- DNA cannot leave the cell because it’s too big.
- A copy of DNA (mRNA) is made, it is a single strand of DNA.
- The part of the gene that is used to code for the protein is located and the DNA unzips around that area, one of strands acts as a template. Complementary bases attach to the strand being copied, (e.g C-G, no Thymine so Adenine attaches to Uracil on the mRNA).
- The mRNA detaches itself and the DNA zips back up.
- mRNA moves out of the nucleus and travels to the ribosomes in the cytoplasm.
16
Q
How is protein made (translation)?
A
- Proteins are made of amino acids, each amino acid is determined by the order of nucleotide bases.
- The ribosome reads the mRNA is order of three bases (called base triplets or codons) as each codon codes for a different amino acid.
- The ribosome reads the triplet code and adds more and more amino acids which join together to make a protein.
17
Q
What are enzymes and their basic function?
A
- Enzymes are made of proteins and are biological catalysts, reducing the need for high temperatures as this can speed up the reactions of unwanted ones.
- Enzymes are not used up or changed during a chemical reaction.
- E.g. used in digestion to break down molecules into smaller ones.
18
Q
Explain the lock and key hypothesis.
A
- Enzymes are folded to form a specific shape, the shape of an enzyme is called an active site.
- Enzymes bind to substrates and a product is formed, after the product is formed the enzyme is free to catalyse another reaction.
- Enzymes have high specificity for their substrate, meaning that they only fit a certain substrate.
19
Q
How does temperature affect enzyme reactions?
A
- As temperature rises the rate of reaction increases up until optimum temperature, this is because the enzymes and substrates move around faster and bind quicker.
- If the temperature gets too high the enzyme will denature and cannot bind with a substrate so rate of reaction rapidly decreases, this denaturing is irreversible.
20
Q
How does pH affect enzyme reactions?
A
- Each enzyme has its own optimum pH, a change in pH can interfere with the amino acids in the enzyme causing it to change shape and denature.
21
Q
How does enzyme concentration affect enzyme reactions?
A
- The more enzyme molecules the more likely it is to bond with the substrate
- Once the substrates have been used up, the rate of reaction slows down.
22
Q
How does substrate concentration affect enzyme reactions?
A
- It increases the rate of reaction until all the active sites are full, so adding more substrates won’t speed the reaction up.
23
Q
What is your metabolic rate?
A
- The speed at which chemical reactions in your cells transfer energy from its chemical stores to food.
24
Q
What are carbohydrates?
A
- Made of CHO.
- Monomers, e.g maltose or glucose
- Polymers are chains of monomers (complex carbohydrates)
25
What are lipids?
- Fats and oils
- Glycerol and three fatty acids.
- Cho
- Not polymers
- provide insulation and buoyancy, also a good store of energy.
26
What is respiration?
Process of transferring energy from the breakdown of glucose.
27
Word equation for for aerobic respiration
glucose + oxygen > carbon dioxide + water
28
What is aerobic respiration and its process?
- Aerobic respiration requires oxygen, it is the most efficient way to transfer energy from glucose.
- The energy produced cannot be directly used to it is transferred to ATP molecules (38 molecules per glucose molecule.)which stores the energy for many cell processes.
29
Where does respiration take place?
In the mitochondria and is controlled by enzymes, it is exothermic.
30
What is anaerobic respiration?
- When doing strenuous excercise your heart and breathing rate aren't fast enough to provide the oxygen needed for aerobic respiration to give you the energy required.
- Transfer of energy without oxygen for short periods of time.
31
Word equation for for anaerobic respiration
glucose > lactic acid. Lactic acid is not completely broken down so a poison is released.
32
Why normally aspire aerobically?
- More ATP per glucose molecule (only 2/glucose molecule in anaerobic respiration)
- Lactic acid causes cramp when building up, causes pain and muscles stop contracting (fatigue).
33
Give examples of organisms performing anaerobic respiration.
- Roots of plants in waterlogged soil due to lack of oxygen.
| - Anaerobic respiration in microorganisms produce ethanol and CO2 (fermentation).
34
Fermentation word equation
glucose > ethanol + carbon dioxide
35
Describe the process of photosynthesis.
Carbon dioxide is taken through via the stoma, water is absorbed from the roots through osmosis, light transfers energy from the sun to chlorophyll in the chloroplasts in stems and leaves where photosynthesis occurs. The products are glucose and oxygen.
36
What are the two stages of photosynthesis?
Stage 1 - energy transferred from light splits water molecules into oxygen gas and hydrogen ions
Stage 2 - carbon dioxide combines with hydrogen ions to make glucose.
37
Uses of glucose in plants
- Cellulose to form cell walls
- Stores food as starch
- Respiration
- + N2 - proteins for growth and repair
- Sucrose stored in fruits
38
Testing for starch in a plant
- Take a leaf, place in boiling water to kill it.
- Place into boiling ethanol to remove the chlorophyll
- Wash leaf to remove the ethanol
- Add drops of iodine, if starch is present it will go from yellow-brown to blue-black.
39
Proving light is needed for photosynthesis.
- Cover a leaf with black card on an area
- Place in the sunlight
- Remove and test for starch, you should see a distinct difference between the area covered and not.
40
What is a limiting factor?
A factor that affects photosynthesis in short supply, thus limiting photosynthesis.
41
What factors affect photosynthesis?
- Light intensity
- Carbon dioxide concentration
- Temperature
42
How do each of these factors affect rate of photosynthesis?
- Light intensity - as light intensity increases so does R.O.P, until a limiting factor makes it plateau
- Carbon dioxide - same as light intensity
- Temperature - Photosynthesis is enzyme controlled so it increases until the temperature is too high and the enzymes denature reducing the rate of photosynthesis,
43
What is the inverse square law and what does it show you?
as you double distance from light source, light intensity falls by a factor of 4
1/d^2
44
How do you prove oxygen is given off in photosynthesis?
Place elodea (pond-weed) (aquatic plant) in water with an upturned test tube above the plant, wait for gas to collect, to see if it is oxygen place a glowing splint in the tube, it should relight.
Biology GCSE
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