Topic 1-Cell biology (cell structure and cell division) Flashcards Preview

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Flashcards in Topic 1-Cell biology (cell structure and cell division) Deck (109):
1

What are all living things made from?

All living things are made of cells. Cells are the basic unit of all forms of life.

2

What two types of cells are there?

Cells can be either PROKARYOTIC or EUKARYOTIC.

3

What are the differences between eukaryotic cells and prokaryotic cells?

Eukaryotic cells are COMPLEX and include all animal and plant cells. Prokaryotic cells are SMALLER and SIMPLER, e.g. bacteria.

4

What are eukaryotes and a prokaryote?

EUKARYOTES are organisms that are made up of eukaryotic cells.
A PROKARYOTE is a prokaryotic cell (it is a single-celled organism).

5

What is the sub cellular structure of most animals?

* Animal cells are eukaryotic.

1) NUCLEUS- contains genetic material that controls the activities of the cell.

2) CYTOPLASM- a gel-like substance where most chemical reactions happen. It contains enzymes that control these reactions.

3) CELL MEMBRANE- holds the cell together and controls what goes in and out.

4) MITOCHONDRIA- these are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work.

5) RIBOSOMES- these are where proteins are made in a cell.

6

What is the sub-cellular structure of most plant cells?

Plant cells usually have all the bits that animal cells have plus a few extra:

1) CELL WALL- a rigid structure made of cellulose. It supports and strengthens the cell. The cells of algae (e.g. seaweed) also have a rigid cell wall.

2) PERMANENT VACUOLE- contains cell sap, a weak solution of sugar and salts. This helps the cell remain turgid.

3) CHLOROPLASTS- these are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.

*The cells of algae (e.g. seaweed) also have a rigid cell wall and chloroplasts.

7

What is the structure of bacterial cells?

BACTERIAL cells are PROKARYOTIC. They are SMALLER than eukaryotes.

A bacterial cell has CYTOPLASM and a CELL MEMBRANE surrounded by a CELL WALL.

Bacterial cells don't have a 'true' nucleus-instead they have a single circular strand of DNA that coats freely in the cytoplasm.

They may also contain one or more small rings of DNA called PLASMIDS.

Remember- bacteria don't have chloroplasts or mitochondria.

8

What are plasmids?

-Plasmids are rings of DNA separate from the main DNA in the bacteria.

Each plasmid is made up of just a few genes that will control a few characteristics.

9

What can bacterial cells do to their DNA that animal and plant cells can't?

-Bacteria are able to make copies of their plasmid and share it with other bacterial cells.

10

How can the replication and sharing of plasmids with other bacterial cells be an advantage?

This can be an advantage as the plasmid may have useful genes on it- if the plasmid has a gene for antibiotic resistance in it, and this is passed to another bacteria, the second bacteria will be resistant to the antibiotics too.

This is how antibiotic resistance has developed.

11

Are all cells identical?

In reality the structure of a cell varies according to what job it does.

12

What is microscopy?

Microscopy is the study of very small objects (such as cells) using an instrument called a microscope.

13

What do microscopes allow us to do?
How have microscopy techniques developed over time?

Microscopes let us see things that we can't see with the naked eye.
Microscopy techniques we can use have developed over the years as technology and knowledge have improved.

14

How long have microscopes been in use for?

Microscopes have been in use for 350 years.
Early microscopes did not magnify to a great extent and scientists have worked hard to improve this.

15

What is resolution?

Resolution is the ability to distinguish two objects from one another.

16

What is magnification?

Magnification is the ability to enlarge an image.

17

What are two common types of microscopes?

The LIGHT microscope and the ELECTRON microscope.

18

How do light microscopes work?

-Light microscopes use light and lenses to form an imagoes a specimen and magnify it (make it look bigger). They let us see individual cells and large sub-cellular structures, like nuclei.

19

How do electron microscopes work?

Electron microscopes use electrons instead of light to form an image.

20

What are the features of a light microscope?

Advantages:
1) You can use living samples.
2) You can view samples in colour.
3) Much cheaper than electron microscopes.
4) Easier to carry/transport

Disadvantages:
1) Magnify up to 2 thousand times.
2) Light microscopes can only distinguish between points which are 200 nm apart.

21

What are the features of an electron microscope?

Advantages:
1) Can magnify up to 2 million times. (Higher magnification than light microscope).
2) Much higher resolving power/resolution of 0.2 nm, (better than a light microscope).Resolution is the ability to distinguish between two points, so a higher resolution gives a sharper image.
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, e.g. the internal structure of mitochondria and chloroplasts. They even let us see tinier things like ribosomes and plasmids.

Disadvantages:
1) You cannot use living samples.
2) The images are in black and white (pictures are often coloured in or dyed).
3) Cumbersome.

22

What is the formula to calculate the magnification of an image?

Note: image size and real size should have the same units. If they don't you will have to convert them first.

magnification = size of image
___________
size of real object

or

magnification=
eye piece lens magnif x objective lens magnif

Remember it as: I
A M

23

How do you convert between cm to mm and micro metres to millimetres.

cm ---> mm x 10

μm ---> mm ÷ 1000

24

What is the first step to look at a specimen e.g. plant or animal cells under a light microscope?

First you must put the specimen on a microscope slide.

25

What is a slide?

A slide is a strip of clear glass or plastic onto which the specimen is mounted.

26

How do you prepare a slide to view onion cells?

Tip- sometimes you can place the specimen on the slide without it being suspended in liquid-it depends on what you're looking at.

1) Add a DROP OF WATER to the middle of a clean slide.

2) Cut up an onion and separate it out into LAYERS. Use TWEEZERS to peel off some EPIDERMAL TISSUE from the bottom of one of the layers.

3) Using the tweezers, place the epidermal tissue into the WATER on the slide.

4) Add a drop of IODINE SOLUTION. Iodine solution is a STAIN. Stains are used to highlight objects in a cell by adding COLOUR to them.

5) Place a COVER SLIP (a square of thin, transparent plastic or glass) on top. To do this stand the cover slip UPRIGHT on the slide, NEXT TO the water droplet. Then carefully TILT and LOWER it so it covers the specimen. Try NOT to get any AIR BUBBLES under there- they'll OBSTRUCT your view of the specimen.

27

Why are stains used when preparing a slide?

In light microscopes, the beam of light passes through the object being viewed. An image is produced because some parts of the object absorb more light than others. Sometimes the object being viewed is completely transparent, so the whole thing looks white because the light rays just pass straight through. To get around this, stains are used to highlight parts of the object.

28

Explain the steps involved to observe your prepared slide...

1. Clip the SLIDE you've prepared onto the STAGE.

2. Select the LOWEST-POWERED objective lens (i.e. the one that produces the 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.

29

How do you draw your observations?

N.b. Students should be able to use estimations and explain when they should be used to judge the relative size or area of sub-cellular structures. Go to page 29 of cgp book to learn this!

1) Draw what you see under the microscope using a SHARP PENCIL.

2) Make sure your drawing takes up at LEAST HALF of the space available and that it is drawn with CLEAR, UNBROKEN LINES.

3) Your drawing should not include any COLOURING or SHADING.

4) If you are drawing CELLS, the SUB-CELLULAR STRUCTURES should be drawn in PROPORTION.

5) Remember to include a TITLE of what you were observing and write down the MAGNIFICATION that it was observed under.

6) LABEL the IMPORTANT FEATURES of your drawing, using STRAIGHT, UNCROSSED LINES.

30

What is a specialised cell?

A specialised cell is one that performs a specific function. Most cells in an organism are specialised. A cell's structure help it to carry out its function (such as transporting a certain substance or executing a specific task).

While they have most of the same features as other cells, specialised cells have structural adaptations that help them do their jobs.

31

What is differentiation?

Differentiation is the process by which a cell CHANGES to become SPECIALISED for its job.

32

How do cells differentiate?

As cells change, they develop DIFFERENT SUB-CELLULAR STRUCTURES and turn into DIFFERENT TYPES OF CELLS. This allows them to carry out SPECIFIC FUNCTIONS.

33

When does differentiation occur in animal cells?

Most differentiation occurs as an organism DEVELOPS so most animal cells differentiate at an early stage.

34

Can animal cells differentiate at a later stage?

In MOST animal cells, the ability to differentiate is then LOST at an early stage, after they become specialised.

35

What is cell differentiation used for in mature animals?

The cells that differentiate in mature animals are mainly used for REPAIRING old or damaged cells and REPLACING CELLS, such as skin or blood.

36

When do plant cells differentiate?

Plant cells differentiate much later in their development.

37

Do plant cells lose their ability to differentiate?

Many types of plant cells retain the ability to differentiate throughout life.

38

What are undifferentiated cells called?

Some cells are undifferentiated cells- they're called STEM CELLS.

39

How are nerve cells specialised for rapid signalling?

The function of nerve cells is to CARRY ELECTRICAL SIGNALS from one part of the body to another.

1) Has a long axon (which is the central nerve which forms the length of the neurone i.e. nerve fibre) this allows the nerve cell to carry electrical signals LONG DISTANCES.

Lots of dendrites (branched connections) anther ends CONNECT to other nerve cells and form a NETWORK throughout the body.

2) Nerve cells are very active so have lots of MITOCHONDRIA to release energy in aerobic respiration.

3)The nerve cell is covered with a fatty sheath, which insulates the nerve cell and speeds up the nerve impulse.

40

What is the function of a sperm cell?

The function of a sperm is basically to get the male DNA to the female DNA.

41

How are sperm cells specialised for reproduction?

1) The ACROSOME in the head contains enzymes which DIGEST through the egg cell membrane so that the sperm can penetrate an egg.

2) There are a lot of mitochondria in the cell to provide the energy needed to swim and fertilise the egg.

3)The flagellum (tail) enables the sperm to swim.

42

What is the function of a muscle cell?

The function of a muscle cell is to CONTRACT QUICKLY..

43

How are muscle cells specialised?

1) These cells are LONG (so that they have the space to CONTRACT).

2) They contain LOTS OF MITOCHONDRIA to generate the ENERGY needed for contraction.

3) Muscles store glucose in the form of glycogen. Glycogen is the storage compound of glucose. It is used when more energy is needed, and it breaks down to carry out respiration.

44

What is the function of root hair cells?

Root hair cells are specialised for ABSORBING WATER and MINERALS.

45

How are root hair cells specialised for absorbing water and minerals?

Root hair cells are cells on the surface of plant roots, which grow into long "hairs" that stick out into the soil.

1) The long hairs gives the plant a BIG SURFACE AREA for absorbing WATER and MINERAL IONS from the soil.

2) It has a thin cell wall to allow water to pass through easily.

46

What is the function of phloem and xylem?

Phloem and xylem are specialised for transporting substances.

47

How are these tubes formed?

Phloem and xylem cells form phloem and xylem tubes, which transport substances such as food and water around plants. To form the tubes, the cells are long and joined END TO END.

48

What do xylem cells transport and where to?

The function of xylem is to bring water and ions from the roots to the leaves.

49

How are xylem cells adapted to transport water and ions?

1) Xylem cells have a hollow lumen as they are formed from dead cells. Therefore there's lots more room for water to be transported.

2) They form continuous columns.

2) The cells walls are strengthened with a strong, waterproof material called lignin. This enables the cell to stretch and prevents it from collapsing due to pressure.

50

What do phloem cells transport and where to?

Phloem moves food substances from leaves to the rest of the plant.

51

How are phloem cells adapted to transport sugar from the leaves to the rest of the plant?

1) They're made from living cells where the cell wall has broken down between cells to form SIEVE plates that allow sugars to flow freely by TRANSLOCATION.

2) COMPANION CELLS are found either side of phloem cells that have MANY MITOCHONDRIA to transfer energy to phloem cells.

3) Phloem cells have very FEW SUB_CELLULAR STRUCTURES, so that stuff can flow through them.

52

What is the purpose of a nucleus?

Most cells in your body have a nucleus.

The nucleus contains your GENETIC MATERIAL in the form of CHROMOSOMES.

53

What are chromosomes?

Chromosomes are COILED UP lengths of DNA MOLECULES.

54

What are genes?

A gene is a short section of DNA. Each gene codes for a specific protein by specifying the order in which amino acids must be joined together.

55

How many genes are in a chromosome?

Each chromosome carries a LARGE NUMBER of genes.

Different genes CONTROL the development of different CHARACTERISTICS, e.g. hair colour.

56

How many chromosomes are usually in a body cell?

*In body cells the chromosomes are normally found in pairs.

BODY CELLS normally have TWO COPIES of each CHROMOSOME- one from the organism's MOTHER and from its FATHER. So humans have two copies of chromosome one , two copies of chromosome two, etc.

In total there are 23 pair of chromosomes.

57

How do body cells divide?

BODY CELLS in MULTICELLULAR organisms DIVIDE to produce new cells as part of a series of stages called the CELL CYCLE.

58

When does the cell cycle start and end?

The cell cycle starts when a cell has been PRODUCED by cell division and ends with the cell dividing to produce TWO IDENTICAL cells, with the same number of chromosomes.

It can be summarised as a stage of cell GROWTH and DNA REPLICATION, followed by a stage of cell DIVISION.

59

What is mitosis?

The stage of the cell cycle when a cell divides is called MITOSIS:

*Mitosis is when a cell reproduces itself by splitting to form two identical offspring.

60

What do multicellular organisms use mitosis for?

Multicellular organisms use mitosis to GROW or REPLACE CELLS that have been DAMAGED.

61

What are the two main stages of the cell cycle?

The two main stages of the cell cycle are:

-Growth and DNA Replication.

-Mitosis

62

Describe the stages of growth and DNA replication...

1) In a cell that's not dividing, the DNA is all spread out in LONG STRINGS.

2) Before it divides, the cell has to GROW and INCREASE the amount of SUB-CELLULAR STRUCTURES such as MITOCHONDRIA and RIBOSOMES.

3) It then DUPLICATES its DNA- so there's one copy for each new cell. The DNA is copied and forms X-SHAPED chromosomes. (Each 'arm' of the chromosome is an EXACT DUPLICATE of the other.)

63

Describe the stages of mitosis...

Once its contents and DNA have been copied, the cell is ready for mitosis...

4) 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.

5) MEMBRANES form around each of the sets of chromosomes. These become the NUCLEI of the two new cells- the NUCLEUS has DIVIDED.

6) Lastly, the CYTOPLASM and CELL MEMBRANE divide.

64

What is the end result of mitosis?

The cell has now produced TWO NEW DAUGHTER CELLS. The daughter cells contain exactly the SAME DNA-they're IDENTICAL.

Their DNA is also IDENTICAL to the PARENT CELL.

65

How do prokaryotic cells replicate?

Prokaryotic cells, such as bacteria, replicate by a type os simple cell division called BINARY FISSION.

In binary fission, the cell makes copies of its genetic material, before splitting into two new daughter cells.

66

What are the stages of the process of binary fission?

Step 1- The CIRCULAR DNA and plasmid(s) REPLICATE.

Step 2- The cell gets bigger and the CIRCULAR DNA STRANDS move to OPPOSITE 'POLES' (ends).

Step 3- The CYTOPLASM begins to DIVIDE and NEW CELL WALLS begin to form.

Step 4- The cytoplasm DIVIDES and two DAUGHTER CELLS are produced. Each daughter cell has ONE COPY of the CIRCULAR DNA, but can have a VARIABLE number of copies of the PLASMID(s).

67

How long does it take for bacteria cells to replicate?

Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.

68

What affects bacteria replication?

- Temperature (too hot or cold and bacteria will denature)
- Availability of nutrients
- The Ph

69

How can you estimate the number of bacteria in a population?

If you want to estimate the number of bacteria in a population, you need to use the MEAN DIVISION TIME.

70

What is the mean division time?

The mean division time is just the AVERAGE AMOUNT OF TIME it takes for ONE BACTERIAL CELL to DIVIDE into two. If you know the mean division time of a cell, you can work out HOW MAANY times it has divided in a certain amount of time, and so the NUMBER OF CELLS it has produced in that time.

71

What are pathogens?

Pathogens are MICRO-ORGANISMS (such as bacteria and viruses) that cause DISEASE.

72

What are bacteria grown in/on?

-Bacteria (and some other microorganisms) are grown (cultured) in a CULTURE MEDIUM, which contains the CARBOHYDRATES, MINERALS, PROTEINS and VITAMINS they need to grow.

-Bacteria can be grown in a NUTRIENT BROTH SOLUTION or as colonies on an AGAR JEL plate.

73

What do bacteria grown on agar jelly form?

Bacteria on agar plates will form visible COLONIES on the SURFACE of the jelly, or will SPREAD OUT to give an even covering of bacteria.

74

What temperature are cultures generally incubated at in school labs and why?

In the LAB AT SCHOOL, cultures of microorganisms are not kept ABOVE 25℃, because HARMFUL PATHOGENS (microorganisms that cause disease) are more likely to grow above this temperature.

75

What temperature are cultures incubated in industrial conditions?

In INDUSTRIAL CONDITIONS, cultures are incubated at HIGHER TEMPERATURES so that they can grow a lot faster.

76

How do you make an agar plate?

-To make an agar plate, HOT agar jelly is pored into shallow round plastic dishes called PETRI DISHES.

-When the jelly's cooled and set, INOCULATING LOOPS (wire loops) can be used to TRANSFER microorganisms to the culture medium. Alternatively, a STERILE DROPPING PIPETTE and SPREADER can be used to get an EVEN COVERING of bacteria.

-The microorganisms then MULTIPLY.

77

What is the difference between bacteria and viruses?

Pathogens are microorganisms - such as bacteria and viruses - that cause disease.

-Bacteria are microscopic organisms. Bacteria are living cells and, in favourable conditions, can multiply rapidly. Once inside the body, they release poisons or toxins that make us feel ill.

White blood cells can ingest and destroy pathogens. They can produce antibodies to destroy pathogens, and antitoxins to neutralise toxins.

-Viruses are many times smaller than bacteria. They consist of a fragment of genetic material inside a protective protein coat.

Viruses can only reproduce inside host cells, and they damage the cell when they do this. A virus can get inside a cell and, once there, take over and make hundreds of thousands of copies of itself. Eventually the virus copies fill the whole host cell and burst it open. The viruses are then passed out in the bloodstream, the airways, or by other routes.

78

PRACTICAL-INVESTIGATING THE EFFECT OF ANTIBIOTICS ON BACTERIAL GROWTH

How can you test the action of antibiotics on cultures of bacteria?

1. Place PAPER DISCS soaked in different TYPES (or different concentrations) of ANTIBIOTICS on an agar plate that has an EVEN COVERING of bacteria. Leave some SPACE between the discs.

2. The antibiotic should DIFFUSE into the agar jelly. ANTIBIOTIC-RESISTANT bacteria will continue to GROW on the agar around the paper discs, but NON-RESISTANT strains will DIE. A CLEAR AREA will be left where the bacteria have died-this is called an INHIBITION ZONE.

3. Make sure you use a control. This is a paper disc that has NOT BEEN SOAKED in an antibiotic. Instead, soak it in STERILE WATER. You can then 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 antibiotic ALONE (and not something weird in the paper, for example).

4. Leave the plate for 48 hours at 25℃.

5. The MORE EFFECTIVE the antibiotic is against the bacteria, the LARGER the INHIBITION ZONE will be.

79

Why are uncontaminated cultures of microorganisms required for investigating the action of disinfectants and antibiotics?

CONTAMINATION by UNWANTED microorganisms will AFFECT YOUR RESULTS and can potentially result in the growth of PATHOGENS.

80

What are the 4 steps to ensure cultures are not contaminated?

1) The Petri dishes and culture medium must be STERILISED before use (e.g. by heating to a high temperature) to KILL any UNWANTED MICROORGANISMS that may be lurking on them.

2) If an INOCULATING LOOP is used to transfer the bacteria to the culture medium, it should be STERILISED first by PASSING IT THROUGH A HOT FLAME.

3) After transferring the bacteria, 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 DON- to STOP drops of CONDENSATION falling onto the agar surface.

81

Why must you only lightly tape the petri dish?

It is important that you don't seal up the Petri dish completely before storing it- you need to let some oxygen get into the dish, otherwise you could end up growing some dangerous pathogens.

82

Other than heating to a high temperature how else can equipment be sterilised?

You can sterilise equipment in a machine called an autoclave- it basically steams equipment at high pressure.

83

How can you compare the effectiveness of different antibiotics (or antiseptics) on bacteria?

You can COMPARE the EFFECTIVENESS of different antibiotics (or antiseptics) on bacteria by looking at the RELATIVE SIZES of the INHIBITION ZONES.

The LARGER the inhibition zone around a disc, the MORE EFFECTIVE the antibiotic is against the bacteria.

You can do this BY EYE if there are large enough differences in size. But to get more accurate results it's a good idea to calculate the AREA of the inhibition zones using their DIAMETER.

84

What is the formula to calculate the area of an inhibition zone?

Area = π r2
(pie r squared)

r- is the radius of the inhibition zone, it's equal to half the diameter.

π-is just a number.

85

How can you find the area of a colony?

The equation Area = π r2 used before can be used to calculate the AREA of a bacterial COLONY. You just need to measure the DIAMETER of the colony you are interested in first.

86

What is differentiation?

Differentiation is the process by which a cell CHANGES to become SPECIALISED for its job.

87

What are stem cells?


What can stem cells do?

-Some cells are UNDIFFERENTIATED cells (i.e. they have not yet changed to become specialised for a particular job). These undifferentiated cells are called STEM CELLS.

-They can divide to produce lots MORE undifferentiated cells.

They can also differentiate (develop into different types of cell), depending on what INSTRUCTIONS they're given.

Stem cells are found in both plants and animals.

88

where do all cells develop from?

When do embryonic stem cells first appear?

All cells develop from the ZYGOTE, which GROWS to become an EMBRYO.

Embryonic stem cells first appear about a week after fertilisation.

89

Where are animal stem cells found?

When do embryonic stem cells first appear?

-Stem cells are found in early HUMAN EMBRYOS.

-Embryonic stem cells first appear about a week after fertilisation.

90

What types of cell can embryonic stem cells differentiate into?

They're exciting to doctors and medical researchers because they have the potential to turn into ANY kind of cell at all.

This makes sense- ALL the DIFFERENT TYPES of cell found in a human being have to come from those FEW CELLS in the early embryo.

91

Where are stem cells found in adults?

Adults also have stem cells, but they're only found in certain places, like BONE MARROW.

92

Can adult stem cells differentiate into many cells like embryonic cells?

What types of cell can bone marrow stem cells turn into?

Unlike embryonic stem cells, they CAN'T turn into every type of cell, only certain ones, such as red cells, white cells and platelets in BLOOD.

93

What is the function of stem cells in embryos?

In animals, the fertilised egg divides over and over again through mitosis to produce an embryo. For the first few days all these cells stay as stem cells.

Each stem cell has the potential to develop into any type of cell in the human body.

94

How can stem cells be used in medicine or research?

Stem cells from embryos and bone marrow can be grown in a lab to produce CLONES (GENETICALLY IDENTICAL CELLS) and made to DIFFERENTIATE into specialised cells to use in MEDICINE OR RESEARCH.

95

What is the function of stem cells in bone marrow?

Bone marrow contains stem cells. These stem cells are capable of giving rise to many more cells of the same type. So they can form NEW BONE MARROW and can DIFFERENTIATE to form a number of different cells like new blood cells, e.g. if blood is lost etc.

96

What medical conditions could be treated with use of stem cells?

Treatment with stem cells may be able to help conditions such as DIABETES and PARALYSIS.

This is because they can be used to replace damaged tissues. In a laboratory, stem cells can be given a certain mix of hormones, enzymes and nutrients to encourage them to differentiate into the required cell.

97

How can bone marrow stem cells be used to replace faulty blood cells?

STEM CELlS transferred from the bone marrow of a HEALTHY PERSON can REPLACE FAULTY BLOOD CELLS in the patient who receives them.

98

What are the 2 main problems associated with bone marrow transplants?

The donor has to be COMPATIBLE with the patient. Otherwise the white blood cells produced by the donated bone marrow could ATTACK the patient's body.

There is a risk that VIRUSES can be passed from the donor to the patient and so make them SICKER.

99

How could embryonic stem cells be used to help diabetes and paralysis?

EMBRYONIC STEM CELLS could also be used to REPLACE FAULTY CELLS in sick people- you could make INULIN-PRODUCING CELLS for people with DIABETES, NERVE CELLS for people paralysed by SPINAL INJURIES, and so on.

100

What is therapeutic cloning?

In therapeutic cloning an EMBRYO is produced with the SAME GENES as the patient.

STEM CELLS from the embryo can be transplanted into the patient WITHOUT BEING REJECTED by the patient's immune system.

Once inside the patient, the stem cells can then DIFFERENTIATE to replace cells which have stopped working correctly.

101

What conditions could therapeutic cloning be useful for?

This technique could be useful for a range of medical conditions such as DIABETES or PARALYSIS.

102

What are the risks and problems associated with the use of stem cells?

The use of stem cells has potential risks such as transfer of viral infection, and some people have ETHICAL or RELIGIOUS objections.

103

Compare the features of embryonic and adult stem cells...

Embryonic:
1) Can become most cells.
2)Stable-can undergo lots of divisions.
3)Easy to obtain
4)Possibility of rejection is UNPREDICTABLE.

Adult:
-Can become many but not all cells.
-Less stable-can undergo fewer divisions.
-More difficult to obtain.
-Minimal rejection if obtained and put back into same patient.

104

What are the arguments for the use of embryonic stem cells?

1) An early embryo that has not yet been implanted into the uterus does not have the psychological, emotional or physical properties that we associate with being a person.

2) God wouldn't want people to suffer if there was a treatment available.

3) People deserve a chance to live regardless of cost.

4)This is true of all treatments, but we should try to reduce suffering in the patient.

5)The embryos used in the research are usually UNWANTED ONES from FERTILITY CLINICS which, if they weren't used for research would probably just be DESTROYED.

105

What are the arguments against the use of embryonic stem cells?

1) The embryo is viewed as a person or it is seen as a potential person.

2) Scientists are playing god.

3) Treatment is costly and the NHS could use the money for other treatments.

4) Stem cells might be rejected by the patient and the treatment will not work.

5) Scientists should concentrate more on finding and developing OTHER SOURCES of stem cells, so people could be helped WITHOUT having to use embryos.

(Research is being done into getting stem cells from differentiated adult cells by reprogramming the adult cells back to an undifferentiated stage. However, further research has to be done to ensure this technique is safe for use in medical treatments.)

106

Where are stem cells found in plants?

Undifferentiated stem cells in plants are grouped together in structures called MERISTEMS.

Meristem tissue is found at the GROWING tips of SHOOTS and ROOTS.

107

Describe the function of stem cells in the meristems in plants...

-Meristems in plants can differentiate into any type of plant cell THROUGHOUT THE LIFE of the plant.

-Plant meristems divide to produce cells that INCREASE the HEIGHT of the plant, LENGTH of the ROOTS and girth of the stem.

-They also PRODUCE cells that develop into LEAVES and FLOWERS.

(They are able to differentiate into lots of different types of plant cell, so are allowing the plant to grow.)

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What is the use of meristems?

Stem cells from meristems in plants can be used to produce CLONES of plants QUICKLY and ECONOMICALLY.

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Why is it useful to clone plants?

• RARE SPECIES can be cloned to protect from extinction.

• Crop plants with special FEATURES such as DISEASE RESISTANCE can be cloned to produce large numbers of identical plants for farmers. This increases farmers profits and might benefit shoppers.