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GCSE Biology > Cell Biology > Flashcards

Cell Biology Flashcards

1
Q

What is meant by a eukaryote?

A

DEFINITION: a multicellular organism whose cells contain a membrane-bound nucleus and other membrane-bound organelles.

INFORMATION:
- eukaryotic cells are more complex and larger than prokaryotic cells.

  • Examples of eukaryotes include: Fungi, Protists, Animals and Plants.
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2
Q

What is meant by a prokaryote?

A

DEFINITION: a single-celled organisms that lacks a distinct membrane-bound nucleus and other membrane-bound organelles, eg mitochondria.

INFORMATION:
- A prokaryote is made up of 1 cell.
- Prokaryotes are much simpler and smaller than eukaryotes.

  • They lack a nucleus/DNA is not enclosed in a nucleus - instead, they have a single circular strand of DNA that floats freely in the cytoplasm.
  • They may also contain one or more small rings of DNA called plasmids.
  • They don’t have chloroplasts or mitochondria
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3
Q

Name the 5 structures inside animal cells

A
  • Nucleus
  • Mitochondria
  • Ribosomes
  • Cell membrane
  • Cytoplasm
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4
Q

Name the 5 structures inside plant cells PLUS the extra 3 that are not included in animal cells

A

EXTRA (animal cells don’t have):
- Cell wall
- Chloroplasts
- Permanent vacuole.

SAME (animals do have):
- Nucleus
- Mitochondria
- Ribosomes
- Cell membrane
- Cytoplasm

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5
Q

Name the structures within a bacterial cell

A
  • Cell membrane (P + A)
  • Cytoplasm (P + A)
  • Cell wall (P)
  • Circular strand of DNA (DNA in P+A is enclosed in a nucleus)
  • Plasmid (Not in P+A)

REMEMBER - bacterial/prokaryotic cells LACK mitochondria.

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6
Q

What type of cell contains a plasmid?

A

A bacterial/prokaryotic cell.

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7
Q

What type of cell does not have its DNA enclosed within a nucleus?

A

A bacterial/prokaryotic cell.

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8
Q

Role of Nucleus

A

Contains genetic material (DNA) enclosed in a nuclear membrane that control activities within the cell.

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9
Q

Role of Mitochondria

A

Where aerobic respiration reactions occur - providing energy for cell.

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10
Q

Role of cell membrane

A
  • To hold the cell together and control what enters and leaves the cell.
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11
Q

Role of cytoplasm

A

A liquid/gel like substance in which chemical reactions occur.

The cytoplasm contain enzymes (biological catalysts that speed up the rate of chemical reactions).

The cytoplasm also contains sub-cellular structures e.g ribosomes, mitochondria.

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12
Q

Role of ribosomes

A

The site of protein synthesis, found on the rough endoplasmic reticulum.

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13
Q

Role of cell wall

A

It is made up of cellulose and its role is to provide support and strength to plant cells.

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14
Q

What is the cell wall made of?

A

Cellulose.

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15
Q

Role of permanent vacuole

A
  • stores cell sap and water
  • keep cells turgid
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16
Q

What is the permanent vacuole made of?

A

Cell sap (a weak solution of sugar and salts).

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17
Q

Role of chloroplast

A

The site of photosynthesis for food production in plant cells.

  • contains a green pigment called chlorophyll which absorbs light energy to make food.
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18
Q

What is meant by an order of magnitude

A

A measuring system used to are used to make approximate comparisons of size or quantity.

1 order of magnitude = 10x
2 orders of magnitude = 100x

  • you can work out the number of orders of magnitude by counting the number of 0s.

eg 1000 000 = 6 orders of magnitude

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19
Q

A fox is 40m long and a worm is 0.4m long, how many orders of magnitude larger is the fox to the worm?

A

40/0.4 = 100.

100x = 2 orders of magnitude. (2 0s).

answer = 2 orders of magnitude.

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20
Q

What is meant by a specialised cell?

A

A cell that has differentiated to have developed different sub-cellular structures to help it carry out specific functions.

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21
Q

Give 3 examples of cells that are specialised in animals

A
  • Sperm cells
  • Nerve cells
  • Muscle cells
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22
Q

Give 3 examples of cells that are specialised in plants

A
  • Xylem cells
  • Phloem cells
  • Root hair cells
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23
Q

What is meant by the term ‘specialised’ when describing a cell?

A

When a cell has been specialised it has developed different sub-cellular structures which help it to carry out specific functions.

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24
Q

What is meant by differentiation?

A

The process by which cells in an organism become specialised/adapted for specific functions during the organisms development, by gaining different sub-cellular structures.

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25
Q

What are undifferentiated cells called?

A

Stem cells

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26
Q

Compare the ability of cells to differentiate in a plant compared to an animal

A
  • Most animal cells differentiate at an early stage of animal’s development.
  • Most plant cells retain the ability to differentiate through out their lives.
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27
Q

How are sperm cells specialised?

What are they specialised for and how?

A
  • specialised to carry male’s DNA to the ovum for fertilisation and successful reproduction.

HOW?

1 Streamlined head and long tail; aids swimming by making it easier so fertilisation can occur faster for successful fertilisation and reproduction

2 Many mitochondria; mitochondria is where aerobic respiration occurs, having lots of them means MORE ENERGY is supplied to allow the sperm cell to move and swim for successful fertilisation and reproduction.

3 Digestive enzymes in acrosome; Digestive enzymes allow for the sperm to easily break down the outer layers of the membrane in the egg cell for successful fertilisation and reproduction.

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28
Q

How are Nerve cells specialised?

What are they specialised for and how?

A

Specialised to transmit electrical signals rapidly from one place in the body to another.

HOW?

1 Long axon; means impulses are carried along a greater distance allowing for ES to be rapidly transmitted.

2 Lots of extensions called dendrites; means branched connections can be formed with other nerve cells which increases surface area allowing for ES to be rapidly transmitted.

3 Many mitochondria on nerve endings; this supplies energy to neurotransmitter chemicals which allow for impulses to be passed from one cell to another more efficiently and quickly allowing for ES to be rapidly transmitted.

4 Axon covered in a myelin sheath; myelin insulates axon thus speeding up the rate at which electrical signals are transmitted.

5 Synapses; junctions which allow for ES to be transmitted from on neuron to another.

  • synapses
  • long axon
  • dendrites
  • axon covered in myelin
  • many mitochondria in nerve endings
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29
Q

How are muscle cells specialised?

What are they specialised for and how?

A

Specialised to contract quickly to move bones or squeeze in order to cause movement.

HOW?

1 Contain protein fibres called myosin and actin; which slide over each other/shorten allowing the muscles to contract easily.

2 Many mitochondria; provide energy FROM respiration for efficient contraction

3 Can store glycogen, a form of glucose; used in respiration by mitochondria, to provide energy for efficient contraction.

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30
Q

How are root hair cells specialised?

What are they specialised for and how?

A

Specialised to take up water by osmosis and mineral ions by active transport from soil to roots of plants

HOW?

1 Root hairs; root hair cells are covered in root hairs which created a larger surface area - this increases rate of osmosis and active transport as more water and mineral ions can be taken in from soil to roots of plants.

2 Many mitochondria; this provides energy from respiration for active transport to occur (more mineral ions taken in).

3 Large permanent vacuole; increases the speed of movement of water from soil to the cell (osmosis).

4 No chloroplasts; greater surface area for active transport and osmosis to occur - speeding up the rate.

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31
Q

How are xylem cells specialised?

What are they specialised for and how?

understand: xylem cells - inner walls die to form a hollow tube called XYLEM - so xylem is made from dead cells

A

Specialised to transport water and mineral ions up the plants from the roots and shoots

HOW?

  • Xylem cells have thick walls and lignin. this provides support to plant and can withstand pressure from water movement allowing for efficient transport of water and mineral ions around the plant.
  • Contain lignin; causes the cells to die creating a hollow tubular shape from the REMAINS of the cell wall so water and mineral ions can easily move through.
  • Lack of internal sub-cellular structures; makes it easier for water and minerals to flow through around plant.
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32
Q

How are phloem cells specialised?

What are they specialised for and how?

page 23 and 74 of CGP + watch FSL vid link:

https://www.freesciencelessons.co.uk/gcse-biology-paper-1/cell-biology/plant-cell-specialisatio n/

A

Specialised to carry products of photosynthesis (food) to all parts of plant (bidirectional movement thru translocation).

  • Sieve plates; cell walls of each phloem cell form structures called sieve plates when they break down, this allows for movement of food from cell to cell.
  • Lack internal structures - greater SA for food to transported around plant.
  • Many mitochondria from companion cells; though phloem vessel cells lack internal sub-cellular structures, each phloem vessel cell has a companion cell connected to them by pores. Mitochondria in the companion cells provide energy for phloem vessel cells for movement of substances by translocation.

summary
- companion cells which provide energy from respiration for translocation bc they have mitochondria.
- cell walls form sieve plates so molecules can pass thru.
- Lack internal structures - greater SA

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33
Q

What happens during differentiation of a cell?

A

Specialisation: cells develop different sub-cellular structures which help them to carry out specific functions - so cell becomes specialised.

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34
Q

Why is differentiation important?

A
  • Specialisation.
  • Tissue repair and regeneration.
  • Maintenance of homeostasis.
  • Organism development
  • Adaption to environment
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35
Q

Compare electron microscopes to light microscopes

A

An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

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36
Q

Advantages and disadvantages of light microscopes

A

ADVANTAGES

  • Easier to use (so can be used in schools)
  • cheaper

DISADVANTAGES

  • Lower magnification (can only see larger sub-cellular organisms)
  • Lower resolving power (so lower resolution - cannot see sub-cellular structures in finer detail as lower ability to distinguish between details,)
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37
Q

Advantages and disadvantages of electron microscopes

A

ADVANTAGES
- higher magnification
- higher resolving power than a light microscope.

^^ This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

DISADVANTAGES
- More expensive
- Requires specialist skills.

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38
Q

What is meant by magnifying power?

A

The degree of enlargement or increase in apparent size achieved by a magnifying optical device.

Magnification is the process.

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39
Q

What is meant by resolving power?

A

The ability to distinguish between two points; higher resolution = clearer/sharper image.

Resolution is the process (can be used as a synonym).

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40
Q

formula to calculate magnification:

A

image size/real size

OR

mag of objective lens x mag of eye-piece.

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41
Q

Describe a practical to use a light microscope to observe, draw and label a specimen (must include mention of scale magnification to get full marks)

A

SLIDE PREP

1 - we add a drop of water to the middle of a clean slide (water is added so specimen is suspended and held in place also ensures cover slip stays in place)
2 - Cut up onion w scalpel and use forceps to peel of a thin epidermal layer of tissue (thin layer is used so light can pass through so internal structures can be observed)
3 - Use a mounting needle to place the epidermal layer of tissue into the water on the slide (mounting needle ensures no air bubbles are formed)
4 - Add a drop of iodine solution to the epidermal layer on the water. (iodine solution adds contrast as it reacts with starch in plant cells to form a blue-black colour, this means that internal structures become more visible)
5 - Cover the epidermal layer using a cover slip (to do this, stand the cover slip up right and carefully tilt and lower it until the specimen is covered - try to avoid air bubbles being formed as this will obstruct view of specimen).
6 - Remove any excess liquid and stain (iodine and water) by soaking the slide in a paper towel.

USING THE MICROSCOPE

7 - Place prepared slide in stage of microscope and secure with the clips.
8 - Select the lowest-powered objective lens (the one w the lowest magnification)
9 - Use the coarse adjustment knob to raise the stage until the slide just touches the objective lens - must do this by looking from the side at the stage - DO NOT look thru the objective lens when doing this, bc u can damage the slide).
10- Now you can look into the eye-piece and turn the coarse adjustment knob to move the stage away until the image comes into rough focus.
11- Now adjust the focus for the third time using the fine adjustment knob until you get a clear image of your specimen.
12- If you need to see the slide with a greater magnification change the objective lens to a higher-powered one and re-focus.

DRAWING OBSERVATIONS

  • make a labelled drawing of a few of the cells you can see - label the key sub-cellular structures eg cell wall and nucleus.
  • Ensure sub-cellular structures are in proportion
  • You must do this with a pencil
  • Include a title and magnification scale.
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42
Q

Label microscope

A

Check CGP book

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43
Q

When carrying out biological drawings, eg cells, what 3 things should you always do?

A
  • Label
  • Title
  • Write magnification
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44
Q

Precautions in microscopy experiment x2

A
  • Wear safety goggles when handling iodine.
  • Handle glass slide with care
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45
Q

What do plants cells have that bacterial cells/prokaryotes don’t have?

A
  • Mitochondria
  • Chloroplasts
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46
Q

What do animal cells have the bacterial cells/prokaryotes don’t have?

A
  • Mitochondria.
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47
Q

What is DNA enclosed in, in eukaryotic cells?

A

A nuclear membrane.

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48
Q

What structures are ribosomes found on?

A

On the rough endoplasmic reticulum.

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49
Q

Where is the permanent vacuole found in a plant cell?

A

In the cytoplasm.

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50
Q

To estimate the size of a sub-cellular/cell structure, what should we do?

A

Treat it like a normal shape and use that equation to calculate it.

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51
Q

Using an optical microscope, what can we see and what can we not see? (for plants and animal cells)

A

ANIMAL CELLS, can see:

  • cell membrane
  • cytoplasm
  • nucleus

ANIMAL CELLS, can’t see:

  • ribosomes

PLANT CELLS, can see:

  • cell wall
  • cytoplasm
  • nucleus
  • maybe vacuole and chloroplasts

PLANT CELLS, can’t see:

  • ribosomes
52
Q

To make a magnification scale, what should we do?

A
  • measure diameter of the field of view of cell using a clear ruler and pencil, with units in mm.

or

  • measure using the eyepiece graticule and calibrate with stage micrometer.
  • write the magnification used, eg 100x
53
Q

How is magnification used during the microscopy experiment calculated?

A

Magnification of objective lens x Magnification of eye-piece

54
Q

How do we calculate the magnification when we know the image size and the real size of a specimen?

A

Magnification = image size/real size

55
Q

What are the typical magnification powers of objective lenses?

A

4x 10x and 40x

56
Q

Why do we not initially look through the eyepiece when adjusting the coarse focus to be just above the slide on the stage?

A

We may damage the slide, instead we look from the side of the stage and adjust.

57
Q

What are chromosomes made of?

A

Genes

58
Q

How have microscopy techniques have developed over time?

How has this benefitted science?

A

INITIALLY (remember it is still used in schools) - Optical microscopes = Light microscopes: use light and lenses to form an image of a specimen and magnify it.

NOW - Electron microscopes: use electrons and lenses to form an image of a specimen and magnify it.

  • How has this benefitted science?

An electron microscope has a much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.

59
Q

PMT flashcards (rp and main)

A

check

60
Q

How would you measure the length of a cell view under a microscope?

A

measure using the eyepiece graticule and calibrate with stage micrometer.

61
Q

What is meant by differentiation?

A

The process by which cells in an organism become specialised for a specific function during the organism’s development.

62
Q

Where are xylem plants found?

A

In the plant stem.

63
Q

How do bacteria multiply/reproduce?

A

Binary fission

64
Q

What is meant by binary fission?

A

When one bacterial cell splits into two bacterial cells.

65
Q

How many times can bacteria carry out binary fission if conditions are favourable?

A

Once every 20 minutes, so long as conditions are favourable, ie enough nutrients and suitable temperature.

66
Q

Give a short summary of what happens during binary fission:

A
  • Circular DNA and Plasmids replicate
  • The cell gets bigger and the circular DNA strands move to opposite ends of the cell.
  • The cytoplasm begins to divide and new cell wall form.
  • The cytoplasm divides completely and two daughter cells are produced.
  • Each (genetically identical to each other and parents, assuming no mutations occurred during the process) daughter cell has one copy of the circular DNA but can have a variable number of the plasmids.
67
Q

Formula to calculate the number of bacteria in a given round:

A

no. of bacteria in a given time = 2^n

where n = number of rounds of division

REMEMBER TO GIVE YOUR ANSWER IN STANDARD FORM!

68
Q

Describe a practical to investigate the effect of different antiseptics or antibiotics on bacterial growth using agar plates by measuring the zones of inhibition

A
  • Clean bench with disinfectant solution to kill unwanted microorganisms to prevent contamination of the culture.
  • Sterilise the inoculating loop by passing it through a Bunsen Burner flame.
  • Open a sterile agar gel plate near a Bunsen burner flame, the flame kills bacteria in the air further preventing contamination.
  • Use the inoculating loop to spread the chosen bacteria evenly over the plate.
  • Place sterile filter paper discs containing antibiotic onto the plate.
  • Incubate the plate at 25 degrees in an incubator.
  • Leave the plate for 2-3 days.
  • Bacterial plate should look like this: draw
  • Around the antibiotic discs there is a region where bacteria has not grown called the zone of inhibition.
  • We can measure the effect of antibiotic by calculating the area of the zone of inhibition (Pi r squared, where r is the radius of the zone of inhibition)
  • Larger area of zone of inhibition (usually white area) means more effective antibiotic.
69
Q

State 2 safety precautions for the microbiology practical:

A
  • Wear safety goggles when handling disinfectant.
  • Wash hands before and after handling the bacteria.
70
Q

Describe how to prepare an uncontaminated culture using aseptic technique.

key words; sterilise, contamination

A
  • Sterilise Petri dishes and culture media such as nutrient broth solution and agar in order to kill unwanted microorganisms to prevent contamination.
  • Sterilise inoculating loop using a flame such as a Bunsen burner flame in order to kill unwanted microorganisms and prevent contamination
  • Attach the lid of the Petri dish to the plate using adhesive tape in order to stop the lid from falling off to prevent unwanted microorganisms from entering and contamination from occurring.
  • Incubate the bacteria in agar gel plate at 25 degrees Celsius to reduce the chances of harmful bacteria growing.
71
Q

Explain why petri dishes and culture media must be sterilised before use

A

In order to kill unwanted microorganisms and prevent contamination.

This is often done in an autoclave (an oven) or by UV light.

72
Q

Explain why inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame

A

In order to kill unwanted microorganisms and prevent contamination.

73
Q

Explain why the lid of the Petri dish should be secured with adhesive tape and stored upside down.

A

In order to prevent unwanted microorganisms from entering and contamination from occurring.

74
Q

Explain why in school laboratories, cultures should generally be incubated at 25°C.

A

In order to reduce the chances of harmful bacteria growing.

75
Q

What does the bacteria culture medium contain ie nutrient broth solution or agar gel plate.

A
  • Nutrients eg carbohydrate and protein, vitamins and minerals.
76
Q

Where is genetic information found in a cell?

A

In the nucleus.

  • Nucleus contains genetic information (DNA).
  • DNA is found in chromosomes (so chromosomes are made from DNA)
  • A gene is a SECTION of DNA
76
Q

In animal cells, how many pairs of DNA are there?

A

23 pairs of chromosomes = 46 in total

23 inherited from each gamete.

77
Q

In gametes, how many chromosomes are there?

A

23 single chromosomes.

78
Q

In body cells, how are chromosomes found?

A

In pairs

79
Q

Explain what happens during the cell cycle including mitosis?

A

STAGE 1; interphase

cell grows, organelles such as ribosomes and mitochondria increase in number and DNA replicates to form 2 copies of each chromosome in an ‘X’ shape.

STAGE 2; Mitosis

chromosomes line up at the equator of the cell and cell fibres pull each chromosome from each pair to either side of the cell and the nucleus divides into 2.

STAGE 3; Cytokinesis

Cytoplasm and the cell membrane divide into two and 2 identical daughter cells are formed. Each daughter cell is genetically identical to each other and their parent cell.

80
Q

What happens during the mitosis stage of the cell cycle?

A

Chromosomes line up at the equator of the cell and cell fibres pull each chromosome of X to either side of the cell, and nucleus divides into two.

81
Q

Explain why cell division by mitosis is important.

A
  • growth and development of multicellular organisms.
  • replacing damaged cells in multicellular organisms.
  • essential for asexual reproduction
82
Q

What is meant by a stem cell?

A

An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.

83
Q

Where can stem cells be found in humans?

A
  • In embryos
  • In bone marrow
84
Q

Explain what is meant by an embryonic stem cell.

A
  • When a sperm and ovum fuse together during fertilisation a fertilised ovum is formed.
  • This fertilised ovum divides by mitosis into a ball of cells can an embryo.
  • The cells within the embryo can differentiate to form specialised cells such as nerve cells, but before they become specialised they have the ability to differentiate into ANY cell.
  • So a cell within an embryo before specialisation is called an embryonic stem cell
85
Q

True or False, adult stem cells such as bone marrow can form ANY type of cell?

A

False.

Their differentiation potential is limited to cell types within their specific lineage or tissue type. eg an adult stem cell found in bone marrow will only be able to differentiate to RBC WBC and platelets,

86
Q

What type of cells can stem cells found in bone marrow differentiate to become?

A

Red blood cells, white blood cells and platelets.

87
Q

How can a person with leukaemia (cancer of the bone marrow) be treated using stem cells?

A
  • Existing bone marrow is destroyed by radiation.
  • Patient receives a transplant of bone marrow from a donor.
  • Stem cells within the bone marrow divide to form new bone marrow and can differentiate to form new RBC WBC and platelets.
88
Q

Issues with bone marrow transplants x 2

A
  • Patient must be compatible with donor or WBC produced by bone marrow will attack patients body
  • Viruses can be passed from donor to patient resulting in illness.
89
Q

How can adult stem cells be used in medicine?

A
  • Tissue/lineage transplant
  • stem cells within tissue divide + replace and differentiate

eg
- Stem cells from adult bone marrow can form many types of cells including blood cells.

90
Q

How can embryonic stem cells be used in medicine

A

THERAPEUTIC CLONING:

Stem cells from human embryos are cloned by scientists to become genetically identical to a patients own cells

These stem cells can be transplanted into the human without being rejected by the patient’s immune system.

Once inside the body, the stem cells can differentiate to many human cells to replace ones that have stopped working properly

eg:

  • Insulin producing cells for ppl w diabetes.
  • Neural cells for people with Alzheimer’s or spinal cord paralysis .
91
Q

Summarise therapeutic cloning in three steps

A

Stem cells from human embryos are cloned by scientists to become genetically identical to a patients own cells

These stem cells can be transplanted into the human without being rejected by the patient’s immune system.

Once inside the body, the stem cells can differentiate to many human cells to replace ones that have stopped working properly.

92
Q

Evaluate the pros and cons of therapeutic cloning (6 marks)

evaluate so must include a justification.

A

Pros of Therapeutic Cloning:

Personalised Treatment:
can produce cells and tissues that are genetically identical to the patient, reducing the risk of rejection by immune system and increasing the effectiveness of treatment.

Treatment for Various Diseases: It holds potential for treating a wide range of diseases and injuries diabetes, spinal cord injuries, and heart disease.

Scientific Research: It allows scientists to study diseases and develop new treatments more effectively by creating disease models using cloned cells.

Unwanted embryos can be used instead of discarded (more ethical)

Cons of Therapeutic Cloning:

Ethical Concerns: There are ethical concerns about the creation and destruction of human embryos during the process of therapeutic cloning.

Technical Challenges: Therapeutic cloning involves complex techniques that are difficult to master, leading to high costs and low success rates.

Risk of Abnormalities: Cloned cells may have genetic abnormalities or mutations or viruses, which could pose risks to the patient’s health when transplanted into the patient.

Overall, while therapeutic cloning offers promising medical benefits, it is accompanied by ethical considerations and technical challenges that need to be carefully addressed.

93
Q

Where are stem cells found in plants (meristematic)?

A
  • Roots
  • Buds/Shoot tips

these contain meristem tissue which are made up of meristematic cells (stem cells)

94
Q

What are meristematic cells

A

Stem cells found in the meristem tissue of plants, located in their roots and buds.

They can differentiate into any type of plant and have the ability to do this THROUGHOUT their life.

An advantage:

They can be used to make clones of the plant, when plant may have desirable features, for research or to prevent extinction of plant.

95
Q

What is meant by diffusion?

A

the spreading out of the particles resulting in a net movement from an area of higher concentration to an area of lower concentration.

96
Q

State and explain 3 examples of diffusion that occurs in animals:

A

1 - Diffusion of O2 from blood into cells.

Oxygen is used mitochondria to generate energy from respiration.
O2 is transported in blood stream, from diffusion thru alveoli in lungs so blood contains a higher conc of O2 than cells.
This means O2 moves from a higher conc (in blood) to an area of lower conc (in cells) to enter cells.

2 - Diffusion of CO2 from cells to the bloodstream.

CO2 is a waste product produced from respiration that occurs inside the cells.

So cells have a higher conc of CO2 than blood stream.

So diffusion of CO2 occurs when CO2 particles move from an area of higher conc to lower conc (blood).

3 - Urea (waste)

Diffuses from liver cells (higher conc) to blood plasma (lower conc) to be transported to the kidney fro excretion.

97
Q

True or false diffusion can occur with large molecules?

Include examples (small enough molecules and too large).

A

False, for diffusion to occur, molecules must be small enough.

So O2 C6H12O6 CO2 and amino acids are small enough but starch and proteins can’t

98
Q

What are the factors affecting the rate of diffusion?

A
  • Concentration gradient (the larger the conc. gradient, the greater the rate of diffusion bc there are more particles moving down the conc gradient than against it )
  • Temperature (the higher the temp, the greater the KE: more KE = more movement = more collisions = faster rate of diffusion)
  • Surface area of membrane (the greater the SA the greater the rate of diffusion bc there’s a greater space for particles to spread from H conc to L conc)
99
Q

Explain the need for exchange surfaces and a transport system in multicellular organisms.

A

Multicellular organisms are very large in size.

This means they have a lower SA to volume ratio, so cannot rely on diffusion alone to meet their metabolic needs.

So they have internal exchange surfaces, transport systems and adaptations to allow molecules to be sufficiently transported into and out of cells.

100
Q

Why can single-celled organisms rely on just diffusion for exchange and transport of substances in their body?

A
  • They are very small so have a relatively large SA:Vol ratio.
  • They have low metabolic demands as they are very simple, so diffusion across the surface of an organism is enough to meet its needs
101
Q

Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials.

A

Organisation, review.

102
Q

How are gills in fish adapted for exchanging materials? (6 marks)

A
  • Fish gills are covered in gill filament and gill lamellae. This creates a larger surface area for diffusion to occur at a faster rate.
  • Fish Gills have a thin membrane. This shortens the distance that diffusion of molecules occur into and out of the blood, allowing diffusion to occur at a faster rate.
  • Fish Gills also have efficient blood supply. This allows for oxygenated blood to be taken away quickly this maintaining a steep conc gradient. This therefore increases the rate of diffusion
103
Q

What is meant by osmosis?

A

Osmosis is the diffusion of water from a dilute solution to a concentrated solution across a partially permeable membrane.

104
Q

What is meant by a partially permeable membrane?

A

A membrane/barrier that allows some molecules to pass through it but not all.

105
Q

True or false, osmosis is passive? Explain your answer.

A

True. Osmosis does not require energy as it goes along the concentration gradient (not against it).

106
Q

Is the cytoplasm of a cell concentrated or dilute in terms of sugar?

A

The cytoplasm is concentrated (has a high concentration of sugar molecules).

107
Q

If a cell is placed in a very concentrated solution of sugar what will happen to it?

What will the solution be described as?

A

The cell will become flaccid (shrivelled).

Because water moves from cell out into solution via osmosis from an area of high concentration of water particles to an area of low concentration of water particles.

The solution would be described as hypotonic to the cell.

108
Q

If a cell is placed in a very dilute solution, what will happen to it?

A

The cell will become turgid.

Because water will move by osmosis from an area of high concentration of water particles to an area of low concentration of water particles.

solution is hypertonic to the cell.

Cell won’t burst because the cell wall will prevent the plant from bursting.

109
Q

Describe what will happen to a cell if it is place in an isotonic solution

A

The cell will remain the same.

Because water will not move into the cell via osmosis.

Because the conc. of water particles inside and outside the cytoplasm is the same.

So there is no conc gradient (osmosis can’t occur).

110
Q

Why must the conc. of water be kept at a certain point in animals?

A

So cells don’t shrivel or burst and die.

111
Q

What is meant by active transport?

A

Movement of substances from a more dilute solution to a more concentrated solution against a concentration gradient. This requires energy from respiration.

112
Q

Compare active transport and diffusion (4 marks)

A
  • Both involve substances moving across some form of membrane.
  • Both occur in living organisms
  • Active transport requires energy from respiration, diffusion doesn’t.
  • Active transport occurs against conc. gradient, diffusion doesn’t.
113
Q

Give an example of why active transport is important in animals.

2 marks

A

It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration.

This is important because sugar molecules are used for cellular respiration.

114
Q

Give an example of why active transport is important in plants.

2 marks

A

Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil.
This is important because plants require ions for healthy growth.

115
Q

Describe a practical to investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue.

A
  • First peel the potato to remove the skin, because the skin can affect the rate of osmosis.
  • Use a cork borer to produce three cylinders of potato. Using a cork borer allows for all the cylinders to have the same diameter.
  • Use a scalpel and ruler to carefully trim the 3 cylinders to the same length eg 4 cm (if we use shorter cylinders it will be more difficult to measure the effect of osmosis
  • Measure the original length of each cylinder using a ruler and the mass of each cylinder using a balance, repeat x3 times and find an average and record this.
  • Place each cylinder into a 3 identical separate test tubes.
  • In one cylinder add 10cm^3 of 0.5 molar sugar solution in the second add 10cm^3 0.25 molar sugar solution and in the third test tube add 10cm^3 distilled water.
  • Leave the cylinders overnight to allow osmosis to take place.
  • Next day, remove potato cylinders and gently(don’t press so water isn’t forced out of cells) roll them on a paper towel to remove any surface moisture which could effect the final mass.
  • Finally, measure the length and mass of the cylinders again, plot on a graph and calculate the percentage change in length and mass (change in value/original value) x100.
116
Q

Safety precautions of osmosis experiment

A

Take care when using the scalpel.

117
Q

Why do we use distilled water instead of tap water when investigating the effect of osmosis on a plant tissue?

A

It doesn’t have impurities which could affect the rate of osmosis

118
Q

Why do we remove potato skin?

A

To allow for osmosis to occur at a faster rate

119
Q

Why do we use a cork borer?

A

So each cylinder has an equal diameter so mass can be compared easily.

120
Q

Why do we gently roll?

A

So we don’t press out water from inside the cells of the potato.

121
Q

Observations from potato osmosis experiment.

all 10cm^3
Distilled Water
0.5 molar sugar solution
0.25 molar sugar solution

A
  • water - potato gains mass bc water moves in by osmosis from an area of high conc of water particles to an area of low conc of water particles.
  • 0.5 and 0.25 molar sugar solution/CONCENTRATED SOLUTION, cylinder loses mass because water leaves it by osmosis (high conc of water particles to low conc)
  • where the line crosses the x axis means that there is no change in mass - that is the approx conc of the potato.
122
Q

Suggest why anaerobic respiration is less efficient than aerobic respiration.

A

Glucose isn’t fully oxidised/broken down (1)
So less energy is transferred (1)

123
Q

Why does anaerobic respiration lead to muscle fatigue?

A

Anaerobic respiration produces lactic acid which builds up in muscles preventing efficient contraction.

124
Q

What is meant by oxygen debt?

A

The amount of oxygen needed to convert lactic acid into glucose after anaerobic respiration.

125
Q

Bacteria at end of growth period =

A

1 x 2^n (number of rounds of division, which u work out by dividing minutes, total, by 60 mins).

126
Q

True or false, algal cells have chloroplasts and a nucleus and a cell wall and a cell membrane?

A

True

GCSE Biology (11 decks)

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