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Biology GCSE > B1 Cell level systems > Flashcards

B1 Cell level systems Flashcards

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1
Q

What are the typical features of eukaryotic cells?

A
  • Nucleus with genetic material
  • Complex and relatively large, 10pm-100pm
  • E.g. plant and animal cells
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2
Q

What subcellular structures do all eukaryotic cells have, and what are their functions?

A

Nucleus: controls cell activity, and contains the genetic material in the form of chromosomes
Cell membrane: provides a selective barrier for substances going into or out of the cell, and contains receptor molecules
Cytoplasm: where chemical reactions occur
Mitochondria: contains enzymes for cellular respiration

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3
Q

What additional subcellular structures do plant cells have, and what are their functions?

A

Cell wall: made of cellulose, making wall rigid and supports the cell
Vacuole: full of cell sap keeping the cell rigid and supporting the plant, keeping it upright
Chloroplast: contains chlorophyll which absorbs light for photosynthesis.

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4
Q

What are the typical features of prokaryotic cells?

A
  • No nucleus, DNA floats in the cytoplasm
  • Simple and relatively small, 1pm-10pm
  • e.g. bacterial cells
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5
Q

What subcellular structures do most prokaryotic cells contain?

A

Cell wall - made of peptidoglycan
Cell membrane
Cytoplasm
Genetic material - called a bacterial chromosome

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6
Q

What extra subcellular structures do bacterial cells have, and what are their functions?

A

Flagella: allows the cell to move through liquids
Pili: enables the cell to attach to structures, and can also transfer genetic material between bacteria
Slime capsule: protects bacterium from drying out and from poisonous substances. Helps to stick to smooth surfaces
Plasmid: circular piece of DNA to store extra genes.

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7
Q

How do you observe cells using a light microscope? (6 steps)

A
  1. Move the stage to its lowest position
  2. Select the objective lens with the lowest magnification
  3. Place the prepare slide on stage
  4. Turn the coarse focus
  5. Turn the fine focus
  6. If a higher magnification is required, then repeat with a higher objective lens.
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8
Q

What are the 2 formulae for magnification?

A

Magnification = eyepiece lens X objective lens

Maginification = image size/real size

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9
Q

Which specific organelles do the following stains make easier to observe? Methylene blue, iodine, crystal violet.

A

Methylene blue: nuclei of animal cells
Iodine: plant nuclei
Crystal violet: bacterial cell walls

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10
Q

Define resolution.

A

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

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11
Q

Describe Transmission Electron Microscopes (TEMs)

A

They produce the most magnified images

A beam of electrons passes through a very thin slice of sample. The beam focuses to produce an image

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12
Q

Describe Scanning Electron Microscopes (SEMs)

A

Produce a 3D image of the surface of a sample
A beam of electrons are fired across the surfaces of a specimen. The reflected electrons are collected to produce an image.

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13
Q

Compare light and electron microscopes. (light)

A

Light microscopes:

  • Cheap to buy and operate
  • Simple and portable
  • Have simple sample prep
  • Natural colour unless stained
  • Living or dead specimens
  • 0.2pm (2 X 10^-7m) resolution
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14
Q

Compare light and electron microscopes. (electron)

A

Electron microscopes:

  • expensive to buy and operate
  • large and difficult to move
  • complex sample prep
  • Black and white unles false colour added
  • only dead specimens
  • 0.1nm (1 X 10^-10m) resolution
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15
Q

What shape does DNA form?

A

Double helix from two strands

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16
Q

What is each long molecule of DNA?

A

A chromosome

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17
Q

What is DNA divided up into?

A

Short sections called genes, which code for a specific characteristic, e.g. eye colour

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18
Q

What is each strand of DNA made up of?

A

A polymer of nucleotides

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19
Q

What does each nucleotide consist of and what is a sequence of 3 nucleotides called?

A

Each nucleotide consists of a sugar (deoxyribose), a phosphate and a base. A sequence of 3 nucleotides is called a triplet or a codon.

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20
Q

How many different types of nucelotide are there?

A

4, each containing a different base from: adenine, thymine, cytosine or guanine.

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21
Q

How are the strands held together?

A

The bases hold the strands together since they bond together using complementary base pairing: A-T, C-G. Each base cross links to a base on the opposite strand.

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22
Q

What are the 2 stages of protein synthesis and where do they take place?

A

Transcription in the nucleus and translation in the cytoplasm.

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23
Q

Describe transcription.

A

The section of DNA that codes fo a protein ‘unzips’. A complementary strand of mRNA (messenger RNA) is transcribed and forms on one DNA strand. The mRNA then detaches from the DNA and moves to the ribosomes in the cytoplasm. The DNA ‘zips’ back up.

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24
Q

Describe translation.

A

The mRNA attaches to a ribosome. tRNA (transfer RNA) brings the correct amino acids for each triplet code (each triplet codes for a particular amino acid). The amino acids join together in a chain to make a protein.

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25
What is different about mRNA?
In the mRNA, there is no thymine, so during transcription, adenine, A binds with uracil, U.
26
What do the amino acids determine?
The amino acids determine the protein made, because the chain of amino acids determines how the protein will fold.
27
What are enzymes?
Enzymes are made up of protein and are biological catalysts which speed up reactions without being used up, increasing the rate of chemical reactions inside organisms.
28
What can enzymes do?
They can build larger molecules from smaller ones, e.g. protein synthesis. They can also break down larger molecules into smaller ones, e.g. digestion.
29
How are enzymes folded?
The amino acid chain in the protein is folded to make a shape into which a substrate fits. This shape is the active site.
30
Enzymes are highly specific and only substrate molecules with the correct shape will fit. What is this called?
The lock and key hypothesis.
31
What happens when the substrate and enzyme bind?
They form an enzyme-substrate complex.
32
How does temperature (and pH) affect enzymes?
At higher temperatures, the enzyme and substrate molecules move faster, since they have more kinetic energy, and thus collide more often. Thus as temp increases, so does rate of reaction. However too high temperatures and deviation from optimum pH can cause enzymes to lose their shape and become denatured.
33
What happens when an enzyme becomes denatured?
The amino acid chains unravel and the shape of the active site changes, so the substrate no longer fits.
34
How does substrate concentration affect enzymes?
As substrate concentration increases, the rate of reaction increases to the point where all present enzymes are used - the point of saturation. At this point, increasing substrate concentration no longer affects the rate of reaction.
35
How does enzyme concentration affect enzymes?
As enzyme concentration increases, the rate of reaction increases to the point where all present substrate molecules are being used. There are no more substrates to bind with present enzymes, so the reaction stops, and increasing it no longer affects the rate of reaction.
36
What are taken into a healthy diet?
Carbohydrates, proteins and lipids.
37
What happens to fats to make them easier to digest?
Fats needs to be broken down into small droplets, called emulsification. In the smalle intestine, bile is responsible for emulsifying fats.
38
Describe carbohydrates.
Contain carbon, hydrogen and oxygen atoms. Their monomers are simples sugars like glucose. Carbohydrates are broken down by carbohydrates enzymes in the mouth and small intestine.
39
Describe proteins.
Contain carbon, nitrogen, hydrogen and oxygen atoms. Monomers are amino acids Proteins are broken down by protease enzymes in the stomach and small intestine
40
Describe lipids.
Contain carbon, hydrogen and oxygen atoms. Not polymers —> no repeating units Made of a glycerol molecule and 3 fatty acids Broken down by lipids in the small intestine
41
What is the importance of the breakdown of carbohydrates, proteins and lipids?
Glucose, amino acids and glycerol and fatty acids are transported by the blood to the cells in the body for different reasons. They produce the building blocks to synthesis many different types of molecules that our bodies need to function.
42
What is metabolic rate?
Metabolic rate is the speed at which chemical reactions in your cells transfer energy from its chemical stores in food. The higher this is, the more food you need to eat.
43
Where does cellular respiration happens and what is it controlled by?
Cellular respiration happens inside cells of all animals and plants. It occurs continuously and is controlled by enzymes.
44
What type of reaction is it?
Respiration is an exothermic reaction as it releases energy to the surroundings by heat. The energy is in the form of ATP (adenosine triphosphate)
45
Word and symbol equation for aerobic respiration.
glucose + oxygen → carbon dioxide + water C6H12O6 + 6O2 → 6CO2 + 6H2O
46
Word and symbol equation for anaerobic respiration.
glucose → lactic acid C6H12O6 → 2C3H6O3
47
What can the ATP released from respiration be used for?
The ATP released from respiration can be used: To synthesis molecules For movements To stay warm
48
When does aerobic and anaerobic respiration happen?
Aerobic respiration occurs in the presence of oxygen. Anaerobic respiration occurs without oxygen, when it cannot be delivered to cells fast enough, like during vigorous exercise.
49
What happens when exercise stops?
When exercise stops, there is an oxygen debt, which must be paid back to remove the lactic acid that has accumulated in the cells. This is why breathing rate (panting) is so high.
50
What does lactic acid cause?
Lactic acid causes cramps. When it builds up in muscle cells, it causes pain and muscles stop contracting. This is called fatigue.
51
How do you get rid of lactic acid?
The extra oxygen you inhale through more breathing, reacts with the lactic acid, breaking it down.
52
Word equation for anaerobic respiration in yeast, fermentation.
glucose → carbon dioxide + ethanol
53
What does fermentation do?
Fermentation transfers glucose stores into energy. It occurs in microorganisms like plants and fungi.
54
Differences between aerobic and anaerobic respiration.
Aerobic | Anaerobic Mitochondria. | Cytoplasm Oxygen needed | Oxygen not needed Complete glucose breakdown | incomplete glucose breakdown 38 ATP yield per mol of glucose | 2 yield per mol of glucose 2900kJ released per mole | 120kJ released per mol of glucose
55
What is photosynthesis?
When photosynthetic organisms like green plants and algae make their own food, using energy from the Sun or and artificial light source, to make glucose.
56
What is the glucose made used for?
Some of the glucose is used to make larger complex molecules that the plants need to grow. These make up the organisms biomass. The energy stored in the organisms biomass then goes through the food chain.
57
Where does the reaction occur?
The reaction occurs in the chloroplasts containting chlorophyll, which absorbs light.
58
Word and symbol equation for photosynthesis.
carbon dioxide + water → glucose + oxygen 6CO2 + 6H2O → C6H12O6 + 6O2
59
What happens in the first stage of photosynthesis?
Stage 1: light dependent: energy transferred from light splits water molecules into hydrogen ions and oxygen gas.
60
What happens in the second stage of the reaction?
Stage 2: light independent: carbon dioxide gas combines with hydrogen ions to form glucose.
61
What type of a reaction is photosynthesis and why?
Photosynthesis is an endothermic reaction, as energy from the surroundings is transferred to keep it going.
62
What do photosynthesis experiments test the presence of?
Starch (glucose is immediately turned into starch is unused), chlorophyll, light, carbon dioxide and oxygen. (tests for these substances are in the B7 tab)
63
How do you test for starch?
1. Boil leaf to kill it 2. Soak it in boiling ethanol to remove the chlorophyll 3. Add iodine solution, if starch is present, then colour change from yellow/brown to blue/black
64
How do you test for chlorophyll?
Place a destarched variegated (only some parts with chlorophyll) plant in sunlight for hours. Then test for starch.
65
How do you test for light?
1. Cover part of a destarched leaf with black card so light cannot reach that area. 2. Place in sunlight for several hours 3. Remove card and test for starch, covered parts should stay yellow
66
How do you test for carbon dioxide?
1. Place a destarched plant inside a polythene bag 2. Add a pot of soda lime to absorb CO2 and water vapour, then seal the bag 3. Place in sunlight for hours and test for starch
67
How do you test for oxygen?
1. Place an upturned testube above an aquatic plant 2. Ensure there is maximum light 3. Wait for gas to collect in tube 4. Place a glowing splint in a tube to relight due to the oxygen present
68
What experiment did Joseph Priestly conduct?
He proved that plants give off oxygen by keeping 2 rats in 2 separate jars, one with a plant and one without. The one with the plant survived but the other one did not. Nowadays ethical factors are considered.
69
What are the limiting factors of photosynthesis?
Light intensity, carbon dioxide concentration and temperature.
70
Describe the effect of light intensity on photosynthesis.
The higher the light intensity, the faster the rate of photosynthesis. This continues until maximum rate.
71
Describe the effect of carbon dioxide on photosynthesis.
The greater the carbon dioxide concentration, the faster the rate of reaction. CO2 is the most common limiting factor because there is only 0.04% of it in the air.
72
Describe the effect of temperature on photosynthesis.
Because it is an enzyme controlled reaction, the higher the temperature, the faster the rate of reaction until the point of denaturing.
73
Formula for rate.
Rate = 1/time
74
How can rate of photosynthesis be investigated?
By measuring the volume of gas given off per minute.
75
What is the inverse square law?
Light intensity obeys the inverse square law. As distance doubles (X2), light intensity quarters (/4). Relative light intensity = 1/d^2
76
How do you control the limiting factors?
Light intensity: place a light source at different distances CO2 concentration: add different masses of potassium hydrogen carbonate powder to aquatic plant water (because it releases CO2) Temperature: place the apparatus in water baths at different temperatures.
77
What happens when investigating each limiting factor?
You see that at a point, increasing it no longer makes a different to rate. This is because one of the other factors is now in short supply and becomes the limiting factor. This cycle continues as you keep adding more of each factor.

Biology GCSE (4 decks)

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