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Biology GCSE Paper 1 > 1. Cell Biology > Flashcards

1. Cell Biology Flashcards

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1
Q

What are eukaryotic cells?

A

More complex, eg. animal or plant cells.

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2
Q

What are eukaryotes?

A

Organisms made up of eukaryotic cells.

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3
Q

What are prokaryotic cells?

A

Smaller and simpler, eg. bacteria.

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4
Q

What is a prokaryote?

A

A prokaryotic cell (single-celled organism)

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5
Q

What is the function of the nucleus?

A

Contains genetic material that controls the activities of the cell.

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6
Q

What is the cytoplasm?

A

Gel-like substance where most chemical reactions happen. It contains enzymes that control these chemical reactions.

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7
Q

What is the function of the cell membrane?

A

Holds the cell together and controls what goes in and out.

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8
Q

What is the function of the mitochondria?

A

Where most of the reactions for aerobic respiration takes place. Respiration transfers energy that the cell needs to work.

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9
Q

What are ribosomes?

A

Where proteins are made in the cell (protein-synthesis).

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10
Q

What do plant cells contain that animal cells don’t?

A

Cell wall, permanent vacuole and chloroplasts.

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11
Q

What is the function of the rigid cell wall?

A

Made of cellulose. It supports the cell and strengthens it.

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12
Q

What is the function of the permanent vacuole?

A

Contains cell sap, a weak solution of sugars and salts.

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13
Q

What are chloroplasts?

A

Where photosynthesis occurs, which makes food for the plant. They contain chlorophyll (green substance), which absorbs the light needed for photosynthesis.

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14
Q

What are the sub-cellular structures of a bacteria cell?

A

Cytoplasm, cell membrane, cell wall, circular strand of DNA, plasmids.

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15
Q

What don’t bacteria cells contain?

A

Chloroplasts and mitochondria.

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16
Q

What do bacteria cells have instead of a nucleus?

A

Single circular strand of DNA floating freely in the cytoplasm and small rings of DNA called plasmids.

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17
Q

What are light microscopes?

A

Use light and lenses to form an image of a specimen and magnify it. They let us see individual cells and large subcellular structures like nuclei.

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18
Q

What are electron microscopes?

A

Use electrons to form an image. Have a much higher magnification than light microscopes. Also have a higher resolution. Let us see much smaller things in more detail, like internal structures of mitochondria and chloroplasts. Can even see ribosomes and plasmids.

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19
Q

What is resolution?

A

The ability to distinguish between two points, so higher resolution gives a sharper image.

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20
Q

What is the equation for magnification?

A

magnification= image size/real size.

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21
Q

Describe how you would carry out the microscopy practical to view and onion cell?

A
  1. Add a drop of water to the middle of a clean slide.
  2. Cut up and onion and separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers.
  3. Place the epidermal tissue into the water on the slide.
  4. Add a drop of iodine solution as a stain. -used to highlight objects in a cell by adding colour to them.
  5. Place a coverslip on top (carefully tilt lower so it covers the specimen). Try not to get air bubbles as this will obstruct the view of the specimen.
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22
Q

How do you use a light microscope?

A
  1. Clip the slide you’ve prepared onto the stage.
  2. Select the lowest-powered objective lens (lowest magnification).
  3. Use the coarse adjustment knob to move the stage up to just below the objective lens.
  4. Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus.
  5. Adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide.
  6. If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.
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23
Q

What is differentiation?

A

The process by which a cell changes to become specialised for its job.

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24
Q

When does most differentiation occur in an animal cell compared to plant cells?

A

The ability to differentiate is lost at an early stage, after they become specialised. However, lots of plant cells don’t loose this ability.

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25
Q

What are differentiated cells used for in mature animals?

A

Repairing and replacing cells, eg. skin or blood cells.

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26
Q

What are undifferentiated cells called?

A

Stem cells.

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27
Q

How are sperm cells specialised for reproduction?

A

Function is to get the male DNA to the female DNA . It has a long tail and a streamlined head to help it swim to the egg. There are a lot of mitochondria in the cell to help provide the energy needed. It also carries enzymes in its head to digest through the egg cell membrane.

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28
Q

How are nerve cells specialised for rapid signalling?

A

Function is to carry electrical signals from one part of the body to another. These cells are long to cover more distance and have branched connections at their ends to connect to other nerve cells and form a network throughout the body.

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29
Q

How are muscle cells specialised for contraction?

A

Function is to contract quickly. Cells are long so have space to contract and contain lots of mitochondria to generate the energy needed for contraction.

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30
Q

How are phloem and xylem cells specialised for transporting substances?

A

Tubes which transport substances such as food and water around the plant. The cells are long and joined end to end to form the tube. Xylem cells are hollow in the centre and phloem cells have very few subcellular structures so that stuff can flow through them.

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31
Q

What does the nucleus contain?

A

Genetic material in the form of chromosomes.

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32
Q

What do genes do?

A

Control the development of different characteristics.

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33
Q

How many pairs of chromosomes do humans have?

A

23 pairs

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34
Q

What is the cell cycle?

A

When body cells in multicellular organisms divide to produce new cells.

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35
Q

What is mitosis?

A

The stage of the cell cycle when the cell divides.

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36
Q

What is a use of mitosis?

A

To grow or replace cells that have been damaged.

37
Q

Describe the first main stage of the cell cycle.

A

Growth and DNA replication: The cell grows and increases the amount of subcellular strucutres such as mitochondria and ribosomes. It then duplicates its DNA which forms X shaped chromosomes.

38
Q

What happens during mitosis?

A

The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell. Membranes form around each of the sets of chromosomes which become the nuclei of the new cell - the nucleus has divided. Lastly the cytoplasm and cell membrane divide.

39
Q

What is produced as a result of mitosis?

A

Two new daughter cells containing exactly the same DNA with identical DNA to the parent cell.

40
Q

What is binary fisson?

A

How prokaryotic cells replicate.

41
Q

Describe the process of binary fission.

A
  1. The circular DNA and plasmids replicate.
  2. The cell gets bigger and the circular DNA strands move to opposite poles of the cell.
  3. The cytoplasm begins to divide and new cell walls begin to form.
  4. The cytoplasm divides and two daughter cells are produced. Each daughter cell has on copy of the circular DNA, but can have a variable number of copies of the plasmids.
42
Q

What conditions do bacteria divide very quickly?

A

Warm environment with lots of nutients.

43
Q

In the right conditions, how long does it take for some bacteria like E. coli to replicate?

A

20 minutes.

44
Q

Why would a bacteria cell stop dividing?

A

If the conditions become unfavourable the cells will stop dividiing and eventually begin to die.

45
Q

What is mean division time?

A

The average amount of time it takes for one bacteria cell to divide into two. (You can use this to calculate how many times it has divided in a certain amount of time and so the number of cells produced).

46
Q

How can you use the mean division time to find the number of bacteria in a population?

A

Total time dividing/mean division time=number of divisions. 2 to the power of divisions=total bacteria produced.

47
Q

What do culture mediums contain?

A

Carbohydrates, minerals, proteins and vitamins needed to grow.

48
Q

What are examples of culture mediums?

A

Nutrient broth solution or solid agar jelly.

49
Q

How are agar plates used?

A

Hot agar jelly is poured into a shallow round plastic dish (petri dish). When the jelly is cool and set, inoculating loops are used to transfer microorganisms to the culture medium. A sterile dropping pipette and spreader could also be used to get an even covering of bacteria. The microoganisms then multiply.

50
Q

What temperature should culture mediums not be kept above at school?

A

25°C. Harmful pathogens are more likely to grow above this temperature.

51
Q

How can you investigate the effect of antibiotics on bacterial growth?

A
  1. Place paper discs soaked in different types or concentrations of antibiotics on an agar jelly plate that has an even covering of bacteria. Leave some space between the disks.
  2. The antibiotic shoud diffuse into the agar jelly. Antibiotic-resistant bacteria will continue to grow but non-resistant strands will die. A clear area will be left where the bacteria have died called an inhibition zone.
  3. Use a paper disc that has not been soaked in antibiotic as a control, soak it in sterile water instead.
  4. Leave the plate for 48 hours at 25°C.
  5. The more effective the antibiotic is against the bacteria, the lager the inhibition zone will be.
52
Q

Why would you use a control disc in an experiment about the effects of antibiotics on bacteria growth?

A

It allows you to be sure that any difference between the growth of the bacteria around the control disc and around one of the antibiotic discs is due to the effect of the antibiotics alone.

53
Q

How can you avoid contamination in the petri dish?

A
  1. Petri dish and culture medium must be sterilised before use to kill any unwanted micrioorganisms.
  2. If an inoculating loop is used it should be steralised by passing it through a hot flame.
  3. The lid of the petri dish should be lightly taped on to stop microorganisms from the air getting in.
  4. The petri dish should be stored upside down to stop drops of condenstation falling onto the agar surface.
54
Q

How can you compare the effectiveness of different antibiotics?

A

Look at the relative sizes of the inhibition zones. The larger the inhibition zone around the disc, the more effective the antibiotic is against the bacteria.

55
Q

How do you calculate the area of the inhibition zone?

A

Area=πr²

56
Q

Where can stem cells be found?

A

Human embryos or adult bone marrow.

57
Q

What is the difference between embryonic stem cells and adult stem cells?

A

Embryonic stem cells have the ability to differentiate into any kind of cell. Adult stem cells can only turn into certain cells such as red blood cells.

58
Q

How can adult stem cells be used to cure disease?

A

Stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient who recieves them.

59
Q

How can embryonic stem cells be used?

A

Replacing faulty cells in sick people. Can make insulin-producing cells for people with diabetes and nerve cells for people paralysed by spinal injuries.

60
Q

What is theraputic cloning?

A

An embryo is made to have the same genetic information as the patient. This means that they would contain the same genes so won’t be rejected by the patients body if used to replace faulty cells.

61
Q

What are the risks involved with using stem cells in medicine?

A

The stem cells grown in the lab could be contaminated with a virus which could be passed onto the patient making them sicker.

62
Q

Why are people against stem cell research and what are some counter-arguments?

A
  1. Feel each one is a potential human life.
  2. But some feel like curing existing suffering patients is more important than the rights of embryos. People may also feel like the embryos used are usually unwanted ones which would probably end up destroyed.
  3. Campaigners think scientists should concentrate on finding other sources of stem cells.
  4. In some countries stem cells are banned, its allowed in the UK as long as it’s following strict guidlines.
63
Q

Where are stem cells found in plants?

A

Meristems.

64
Q

What can plant stem cells be used for?

A

To produce clones of the plant quickly and cheaply, to grow more rare species to prevent them from being wiped out, to grow crops of identical plants that have desired features for farmers such as disease resistance.

65
Q

What is diffusion?

A

The spreading out of particles from an area of high concentration to an area of lower concentration.

66
Q

What substances does diffusion happen in?

A

Solutions and gases, particles in these substances are free to move randomly.

67
Q

What gives a faster rate of diffusion?

A

Bigger concentration gradient, higher temperature (the particles have more energy so move around faster).

68
Q

How do cell membranes work for diffusion?

A

Only allow small molecules to diffuse through, big molecules can’t fit through. The larger the surface area of the membrane, the faster the rate of diffusion because more particles can pass through at once.

69
Q

What is osmosis?

A

The movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration.

70
Q

How would you carry out an experiment showing the effect of sugar solutions on plant tissue?

A
  1. Cut up a potato into identical cylinders. Get some beakers with different sugar solutions (one pure water, one very concentrated and a few inbetween eg. 0.2mol/dm^3…etc).
  2. Measure the mass of the cylinders, then leave one cylinder in each beaker for around 24 hours.
  3. Take them out and dry them with paper towel and measure their masses again.
  4. If they have drawn in water by osmosis their mass will have increased. In water has been drawn out there would be a decrease in mass. Calculate the percentage change in mass and plot it on a graph.
71
Q

Osmosis practical: Why would you calculate percentage change in mass?

A

You can compare the effect of sugar concentration on cylinders that didn’t have the same initial mass.

72
Q

Osmosis Practical: What are the independent, dependent and control variables?

A

Dependent: Chip’s mass. Independent: concentration of sugar solution. Control: volume of solution, temperature, time, type of sugar…

73
Q

Osmosis Practical: What errors could arise and how could you reduce them?

A

Potato cylinders not fully dried so excess water gives a higher mass. Or if water evaportated from the beakers the concentrations of the sugar solutions would change. You can reduce these errors by repeating the experiment and calculating a mean percentage change at each concentration.

74
Q

What is active transport?

A

The movement of substances from a lower to higher concentration, against a concentration gradient. Needs energy.

75
Q

Why are root hair cells adapted for taking up minerals?

A

Each branch covered in millions of microscopic hairs giving the plant a large surface area for absorbing water and mineral ions needed for healthy growth.

76
Q

Why can’t root hair cells use diffusion to take up minerals from the soil?

A

The concentration of minerals is usually higher in the root hair cell than in the soil around them.

77
Q

How do root hair cells take in minerals using active transport?

A

The plant absorbs minerals from a dilute solution against a concentration gradient. Needs energy from respiration to work.

78
Q

Where does active transport happen in humans?

A

In the gut when there is a lower concentration of nutrients in the gut but a higher concentration of nutrients in the blood. Active transport allows the nutrients to be taken into the blood.

79
Q

Why is active transport in the gut useful?

A

Glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. It can then be transported to cells and used for respiration.

80
Q

Why do cells use diffusion?

A

To take in substances they need and get rid of waste products.

81
Q

What are two examples of cells using diffusion?

A

Gas exchange: oxygen and carbon dioxide are transferred between cells and the environment. And: Urea diffuses from cells into the blood plasma for removal from the body by the kidneys.

82
Q

What defines how easy it is for an organism to exchange substances with its environment?

A

Surface area to volume ratio.

83
Q

Why can gases and dissolved substances in single celled organisms diffuse directly into or out of the cell across the cell membrane?

A

They have a larger surface area compared to their volume so enough substances can be exchange across the membran to supply the volume of the cell.

84
Q

How are exchange surfaces adaptaded to maximise effectiveness?

A

Have a thin membrane so substances have a short distance to diffuse. Have a large surface area so a lot of substances can diffuse at once. In animals, exchange surfaces have lots of blood vessels to get stuff into and out of the blood quickly. Gas exchange surfaces in animals are often ventilated too so air can move in and out.

85
Q

How are the lungs adapted for gas exchange?

A

Job is to transfer oxygen to the blood and remove waste carbon dioxie from it. Lungs contain millions of little air sacs called alveoli where gas exchange takes place.

86
Q

How are alveoli specialised to maximise the diffusion of oxygen and carbon dioxide?

A

Have an enormous surface area, a moist lining for dissolving gases, very thin walls and a good blood supply.

87
Q

How are the villi adapted for absorbtion?

A

Increase surface area so food is absorbed much more quickly into the blood. Have a single layer of surface cells and a good blood supply.

88
Q

How is the leaf’s structure adapted so carbon dioxide can diffuse into the cells for photosynthesis?

A
  1. Underneath of leaf is an exchange surface, covered in stomata which the carbon dioxide can diffuse through.
  2. Oxygen (produced in photosynthesis) and water vapour can diffuse out through the stomata.
  3. The size of the stomata are controlled by guard cells. If the plant is loosing water faster than it is being replaced by the roots then the stomata will be closed to prevent the plant from wilting.
  4. Flattened shape of leaf increases the area of the exchange surface so that it’s more effective.
  5. The walls of the cells from another exchange surface.
  6. The air spaces inside the leaf increase the area of this surface so there is a higher chance of carbon dioxide getting into cells.
89
Q

How are gills adapted for gas exchange in fish?

A
  1. Water that contains oxygen enters the fish through its mouth and passes out through its gills. As this happens, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water.
  2. Each gill is made up of thin plates called gill filaments, which give a big surface area.
  3. Gill filaments are covered in tiny structures called lamellae which further increase surface area. The lamellae also have lots of blood capillaries which speed up diffusion. They also have a thin surface layer of cells to minimise the distance that gases have to diffuse.
  4. Bloof flows through the lamellae in one direction and water flows over in the opposite direction which maintains a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than that in the blood so as much oxygen as possible diffuses from the water into the blood.

Biology GCSE Paper 1 (4 decks)

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