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Biology GCSE OCR Gateway A > B1 - Cell-level systems > Flashcards

B1 - Cell-level systems Flashcards

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1
Q

What are the differences between eukaryotic and prokaryotic cells?

A

Eukaryotic cells:

  • contain genetic material in nucleus
  • are complex and relatively large
  • between 10 to 100 micro-metres

Prokaryotic cells:

  • genetic material floats in the cytoplasm
  • simple and relatively small
  • between 1 to 10 micro-metres
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2
Q

What sub cellular structures do all eukaryotic cells contain?

A

Nucleus - controls the activities of a cell and contains the genetic material arranged as chromosomes
Cell membrane - a selective barrier that controls which substances leave or enter the cell
Mitochondria - where respiration occurs
Cytoplasm - where chemical reactions occur

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3
Q

Plant sub-cellular structures include:

A

Chloroplasts - which contains green chlorophyll which transfers energy from the sun to be used in photosynthesis
Cell wall - surrounds the cell and is made of a tough fibre called cellulose, makes the cell wall rigid and supports the cell
Vacuole - filled with cell sap helping to keep the plant rigid, supporting the plant and keeping it upright

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4
Q

What are the 7 life processes?

A

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition

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5
Q

What are bacteria?

A

Bacteria are unicellular organisms, eg:

  • E-coli, which cause food poisoning
  • Streptoccus bacteria, which causes sore throats
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6
Q

What are flagella and pili?

A

Flagella - ‘tail-like’ structures that allow the cell to move through liquids

Pili - tiny ‘hairlike’ structures that allow the cell to attach itself structures and can also be used to transfer genetic material

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7
Q

What are slime capsules and plasmids?

A

Slime capsule - a layer outside the cell wall which protects a bacterium from drying out and poisonous substances, also helps the bacteria to stick to smooth surfaces

Plasmid - a circular piece of DNA used to store extra genes which may be used in times of stress, an antibiotic resistant gene may be found here

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8
Q

How to observe cells through a light microscope?

A
  1. Move the stage to its lowest position
  2. Select the objective lens with the lowest magnification
  3. Place the slide, which has cells on it, on the stage
  4. Turn the coarse focus knob slowly until you see your object
  5. Turn the fine focus knob slowly until your object comes into clear focus
  6. To see the cells in greater detail, repeat the steps above using a higher magnification objective lens
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9
Q

How to apply a stain?

A
  1. Place the cells on a glass slide
  2. Add one drop of stain
  3. Place a cover slip on top
  4. Tap the cover slip gently with a pencil to remove air bubbles
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11
Q

What is resolution?

A

The smallest distance between two points that can be seen as separate entities

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12
Q

Why stain cells and some examples of stains?

A

Most cells are colourless and are stained to make them easier to observe, examples include:

  • methylene blue, makes it easier to see the nucleus of an animal cell
  • iodine, makes it easier to see plant cell nuclei
  • crystal violet, stains bacteria cell walls
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13
Q

What are transmission electron microscopes (TEM)?

A

They produce the most magnified images:

  • a beam of electrons is passed through a very thin sample
  • the beam is then focused to produce an image
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14
Q

What are scanning electron microscopes ( SEM)?

A

Produce a 3D image of a surface

  • send a beam of electrons across the surface of a specimen
  • reflected electrons are collected to produce an image
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15
Q

Compare light and electron microscopes:

A

Light:

  • cheap to buy and operate
  • small and portable
  • easy to prepare a sample
  • natural colour of a sample can be seen
  • specimens can be living or dead
  • resolution up to 0.2 micrometers

Electron:

  • expensive to buy and operate
  • large and difficult to move
  • sample preparation is complex
  • black and white images produced
  • specimens are dead
  • resolution up to 0.1 nanometers
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16
Q

What are genes and chromosomes?

A

Chromosome - a long molecule of DNA

Gene - A short section of DNA that codes for a protein

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17
Q

What is the structure of DNA?

A
  • Made up of two strands joined together by bases which are then twisted together to form a double helix
  • made up of lots of nucleotide monomers, which is made of a sugar(deoxyribose), a phosphate group and base
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18
Q

How do the bases in DNA bond?

A

Using complimentary base pairing and hydrogen bonds:

  • Adenine bonds with Thymine
  • Cytosine bonds with Guanine
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19
Q

What is transcription?

A

Transcription is the first part of of protein synthesis:

  • DNA around a gene unzips so both strands are separated
  • One of the DNA strands acts as a template
  • Complementary bases attach to the strand being copied
  • C to G, G to C, A to T and there is no thymine in mRNA so Uracil bonds with adenine
  • When complete the mRNA detatches itself and the DNA zips back up
  • The mRNA is small enough to leave the nucleus and then go towards the ribosome
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20
Q

What is translation?

A

Translation is the second part of protein synthesis:

  • The mRNA attaches itself to a ribosome
  • The ribosome reads the nucleotides on the mRNA in groups of 3 (codons). Each triplet codes for a specific amino acid
  • The ribosome continues to ‘read’ the triplet codes adding more and more amino acids
  • The amino acids join together in a chain, this is a protein
21
Q

What are enzymes?

A

Enzymes are biological catalysts made of protein, they speed up a reaction without being used up themselves. For example they can:

  • Build larger molecules from smaller ones (protein synthesis)
  • Break down large molecules into smaller ones (digestion)
22
Q

What do enzymes look like?

A
  • Enzymes are a protein so they are made up of a long chain of amino acids which is folded together to form a specific shape
  • The active site is where the substrate binds to the enzyme
  • The substrate is the molecule that binds to the enzyme
23
Q

How do enzymes work?

A
  • Enzymes are highly specific and can only bind to one type of substrate molecule
  • The substrate molecule fits into the active site(lock and key hypothesis)
  • The enzyme then either breaks it down or forms new bonds
  • Once this is finished the enzyme is free to catalyse another reaction the same as what it just did
24
Q

How does temperature affect enzyme controlled reactions?

A

In general the higher the temperature the faster the enzyme and substrate molecules collide with each other therefore the faster the reaction

  • If the temperature becomes too high, the amino acid chains start to unravel
  • This changes the shape of the active site which means the enzyme is now denatured
  • The substrate can no longer bind so the rate of reaction decreases
  • Once all enzymes are denatured the reaction stops
25
Q

What other factors apart from temperature affect enzyme-controlled reactions?

A
  • pH: every enzyme has an optimum pH, a change in this may result in the enzyme becoming denature
  • Increasing the substrate concentration: This will increase the rate of until all enzymes are being used, then the rate will be steady and the graph will level off
  • Increasing the number of enzymes: This will increase the rate of reaction until there is no more substrate left, then if no new substrate molecules are added the reaction will stop
26
Q

What is the metabolic rate?

A

The speed at which chemical reactions in your cell transfer energy from its chemical stores in food

27
Q

What are carbohydrates and how are they broken down?

A

Carbohydrates are polymers that are made up of smaller sugar molecules. For example starch is an example of a carbohydrate polymer as it’s made up of smaller glucose monomers.

  • Amylase is the enzyme responsible for breaking down starch into smaller glucose molecules
  • Carbohydrase enzymes break down carbohydrates into sugars
28
Q

What are proteins and how are they broken down?

A

Proteins are polymers that are formed from amino acids

- Protease enzymes break down protein into amino acids

29
Q

What are lipids and how are they broken down?

A

Lipids are the fats and oils you eat. They are a good store of energy and can be used as insulation/buoyancy. Lipid is synthesised from 3 fatty acid molecules and a glycerol molecule.
- Lipase enzymes break down lipids into fatty acids and glycerol

30
Q

What is respiration?

A

When glucose reacts with oxygen to produce energy in the form of ATP(adenosine triphosphate). The word equation is:

  • Glucose + Oxygen -> Water + Carbon dioxide + ATP
  • It’s an exothermic reaction as heat is transferred to the surroundings
31
Q

What is ATP/energy used for?

A
  • For movement - ATP is used to contact muscle cells

- To stay warm

32
Q

Where does respiration occur?

A

In the mitochondria that has a folded inner membrane for a larger surface area

  • The amount of mitochondria in a cell shows how active is it
  • Muscle cells have a lot of mitochondria
33
Q

What is anaerobic respiration?

A

When you exercise your heart and breathing rate increase to meet the demand for oxygen. However in strenuous exercise your heart cannot keep up with the demand so your body begins to respire anaerobically:
- Glucose -> lactic acid + ATP
glucose is not fully broken down and poisonous lactic acid is produced

34
Q

Why does the body normally respire aerobically?

A
  • Aerobic respiration produces more ATP per glucose molecule than anaerobic respiration, it has a greater yield.
  • The lactic acid produced in anaerobic respiration can cause cramp, when lactic acids build up in muscle cells it causes pain which stops them contracting.
35
Q

What is oxygen debt?

A

When you finish exercising you keep breathing heavily as the extra oxygen is needed to break down the poisonous lactic acid. The oxygen needed for this process is called oxygen debt

36
Q

What is fermentation?

A

It’s an example of anaerobic respiration:

- Glucose -> Ethanol + Carbon dioxide

37
Q

What is photosynthesis?

A

The process in which plants make glucose.
- Carbon dioxide + Water -> Oxygen + Glucose
uses light and chlorophyll
- It’s an endothermic reaction as energy must be transferred from the surroundings to keep it going
- Some of the waste oxygen is used in respiration, the rest is released back into the environment

38
Q

How does carbon dioxide and water get into the plant?

A
  • Carbon dioxide diffuses from the air into the plant through the stomata
  • Water enters the roots from the soil through the root hair cells by osmosis
39
Q

Where does photosynthesis occur?

A

Photosynthesis takes place inside the plants chloroplasts which means most of it happens in the leafs however a small amount happens in the green stems.

Light transfers energy from the sun to chlorophyll where carbon dioxide and water react to make glucose.

40
Q

What are the two stages of photosynthesis?

A
  • Stage 1 (light dependant) , energy transferred from light splits water into oxygen gas and hydrogen ions
  • Stage 2 (light independent) , carbon dioxide gas combines with the hydrogen ions to make glucose
41
Q

What happens to the glucose produced from photosynthesis?

A
  • Some of the glucose is immediately used in respiration
  • Some of the glucose is converted to other sugar molecules
  • Glucose that isn’t needed is converted to starch, can be used at night for respiration when the plant isn’t photosynthesising
  • Cellulose to form cell walls
42
Q

How can you test for starch?

A
  1. Take the leaf you are going to test and place in a beaker of boiling water for about a minute to kill it.
  2. Then place the leaf into a boiling tube of boiling ethanol to remove all the chlorophyll(water bath as ethanol is flammable)
  3. Then wash the leaf with water to remove ethanol and soften the leaf
  4. Spread it out on a white tile
  5. Add a few drops of iodine solution
    - If starch is present it will turn from yellow-brown to blue-black
43
Q

How do you de-starch a plant?

A

Keep the plant in the dark for a minimum of 24 hours

44
Q

How can you prove chlorophyll is needed for plants?

A

Variegated leaves only have chlorophyll in some area of the plants so they appear to be green or white in places

  • Place a de-starched variegated leaf in the sunlight for several hours then check for the presence of starch
  • Only the green areas of the leaf should turn blue-black
45
Q

How can you prove light is needed for photosynthesis?

A
  • Take a de-starched plant and cover one or part of its leaf with foil or a black card so that light is unable to reach
  • Leave in the sunlight for several hours
  • Then test the leaf for the presence of starch
  • The covered area should not contain any starch
46
Q

How can you prove carbon dioxide is needed for photosynthesis?

A
  • Take a de-starched plant and place it inside a polythene bag
  • Before sealing the bag add a pot of soda lime (this absorbs CO2 and water vapour)
  • Seal the bag and place in the sunlight for several hours
  • Then check the leaves for the presence of starch
47
Q

How can you prove oxygen is given off during photosynthesis?

A

Place an upturned text tube above an aquatic plant, put the apparatus in light for maximum rate of photosynthesis. Once the test tube is full, place a glowing splint inside, it should re light due to the oxygen.

48
Q

What are 3 factors that affect the rate of photosynthesis?

A
  • Light intensity - the higher the light intensity the higher the rate of photosynthesis until it reaches its maximum rate where the graph levels off. In low/no light photosynthesis may stop
  • Carbon dioxide - the more carbon dioxide the faster the rate of reaction until it’s not the limiting factor anymore
  • Temperature - as photosynthesis is a series of enzyme controlled reactions, there is an optimum temperature however if it’s too high the enzymes will denature and the reactions will stop

Biology GCSE OCR Gateway A (6 decks)

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