Cell Biology Flashcards
(100 cards)
1
Q
State the function of the stage.
A
This is where the the microscope slide is placed.
2
Q
State the function of the lamp.
A
This provides illumination. The light from the lamp shines through the specimen and into the objective lens.
3
Q
State the function of the objective lenses.
A
These magnify the object.
4
Q
State the function of the eyepiece.
A
This is where the specimen is viewed. The eyepiece lens has a magnification of 10x.
5
Q
State the function of the coarse focussing lens.
A
This allows us to rapidly move the stage towards and away from the objective lens, focussing the image.
6
Q
State the function of the fine focussing dial.
A
This moves the stage by a very small amount, allowing us to focus on fine detail.
7
Q
Describe how to use a light microscope.
A
-First, we place the slide on a stage and secure it with clips. This prevents the slide from moving around while we are observing the specimen.
-Then, we adjust the objective lens to the lowest power.
-After, we use the coarse focussing dial so that the objective lens is almost touching the slide.
-While we do this, we should look at the microscope from the side rather than the eyepiece to prevent the slide from hitting the objective lens.
-When the objective lens is almost touching the slide, we can look down the eyepiece and use the fine focussing dial until the cells come into focus.
8
Q
Give the equation for magnification.
A
Magnification = size of image/ actual size of object
9
Q
How are millimetres converted to micrometres.
A
Millimetres x1000 = Micrometres
Micrometres/ 1000 = Millimetres
10
Q
Describe how to prepare an animal cheek cell slide.
A
-Use a wooden spatula to scrape the inside of the mouth
-Add the cell tissue to the slide
-Add one small drop of methylene blue
-Cover the slide with a cover slip- try to avoid air bubbles
-Place under a microscope with lowest magnification on first and secure with clips
-Draw a diagram of the observations and add labels
11
Q
Describe how to prepare an onion cell slide.
A
-Place two drops of water on a slide
-Peel off a layer of tissue from the onion and flatten on the slide
-Place two drops of iodine solution on the onion cells
-Cover the slide with a cover slip- try to avoid air bubbles
-Place under a microscope with lowest magnification on first and secure with slips
-Draw a diagram of the observations and add labels
12
Q
Give the Advantages of Light Microscopes.
A
-Small/ portable
-Cheap
-Easy to use
-Used to examine living cells
13
Q
Give the Disadvantages of Light Microscopes
A
-Resolution is limited so they cannot be used to study sub-cellular structures
-Low magnification sizes
14
Q
Give the Advantages of Electron Microscopes.
A
-High resolution so can be used to study sub-cellular structures
-High magnification sizes
15
Q
Give the Disadvantages of Electron Microscopes
A
-Large/difficult to transport
-Expensive
-Hard to use
-Can’t examine living cells
16
Q
State the function of the nucleus.
A
The nucleus controls the activities of the cell and contains the cell’s genetic material.
17
Q
State the function of cytoplasm.
A
Cytoplasm is a watery solution in which other organelles are held and where most chemical reactions in the cell take place.
18
Q
State the function of ribosomes.
A
Ribosomes are where proteins are synthesised in the cell.
19
Q
State the function of the cell membrane.
A
The cell membrane controls the molecules that enter and leave the cell such as glucose or hormones.
20
Q
State the function of mitochondria.
A
Mitochondria is where aerobic respiration takes place in the cell.
21
Q
State the function of the cell wall.
A
The cell wall is made of cellulose. It strengthens the cell and gives it support.
22
Q
State the function of the vacuole.
A
The vacuole is a hole in the cytoplasm filled with sap. It is important for keeping the cell rigid and giving the cell its shape.
23
Q
State the function of chloroplasts.
A
Chloroplasts contain the green pigment chlorophyll. The chlorophyll traps the light energy needed for photosynthesis.
24
Q
State the function of the flagellum.
A
They are long proteins which wave around to help the bacteria to move.
25
State the function of the cytoplasm.
This is where the reactions of the cell take place.
26
State the function of plasmid DNA.
These are small circles of DNA which codes (gives instructions) for specific properties e.g. antibiotic resistance.
27
State the function of free DNA.
This is DNA that controls the cell and is passed on in replication (not in a nucleus).
28
State the function of the cell wall.
This gives the cell its shape (like plants) and is made from sugars and proteins (not cellulose).
29
State the function of the cell membrane.
This controls what enters and leaves the cell. It is a partially permeable membrane.
30
Compare the sizes of eukaryotic and prokaryotic cells.
Eukaryotes:
-most are between 5 and 100 micrometres
Prokaryotes:
-most are between 0.2 and 2 micrometres
31
Compare the outer layers of eukaryotic and prokaryotic cells.
Eukaryotes: cell membrane is surrounded by cell wall (in plants and fungi)
Prokaryotes: cell membrane is surrounded by cell wall
32
Compare the contents of eukaryotic and prokaryotic cells.
Eukaryotes:
- they contain cytoplasm, ribosomes, cell organelles include mitochondria and there are chloroplasts in plants
Prokaryotes:
-they contain cytoplasm and ribosomes, but no mitochondria or chloroplasts
33
Compare the genetic material of eukaryotic and prokaryotic cells.
Eukaryotes:
-DNA in a nucleus - plasmids are found in a few simple eukaryotic organisms
Prokaryotes:
-DNA is a single molecule, found free in the cytoplasm - additional DNA is found on one or more rings called plasmids
34
Compare the type of cell division used by eukaryotic and prokaryotic cells.
Eukaryotes:
-these cells divide by mitosis
Prokaryotes:
-these cells divide by binary fission
35
What are chromosomes and genes?
-A chromosome is a long strand of DNA found in the nucleus. There are 23 pairs of chromosomes which contain genes.
-Genes are a section of DNA coding for a characteristic
36
Describe the stages in the cell cycle.
-The DNA replicates to form two copies of each chromosome. The cell grows and copies its internal structures such as mitochondria and ribosomes
-This is mitosis. One set of chromosomes is pulled to each end of the cell. The nucleus also divides.
-The cytoplasm and cell membrane divide to form two identical cells.
37
Describe three functions of cell division by mitosis.
-Mitosis is required for growth and development e.g. for a growing foetus. This is the case of multicellular organisms (plants and animals including humans)
-Mitosis is required for repair of body tissue e.g. healing the skin if there is a cut
-Mitosis takes place during asexual reproduction. This is when organisms reproduce without the need for a partner. This is apparent in a large number of plants and some animals.
38
Why does the use of mitosis change in mature animals?
Mature animals have stopped growing so it is only needed for healing and repairing the body.
39
What is a specialised cell?
A specialised cell is a cell that performs a specific role in an organism.
40
Describe how a sperm cell is specialised to perform its function.
Long tail- allows the sperm to swim to the ovum
Streamlined shape- makes it easier for the sperm to swim to the ovum
Lots of mitochondria- carry out respiration to provide the energy required for swimming
Enzymes- Required to digest the outer layer of the ovum so the sperm's nucleus can pass into the ovum
41
Describe how a nerve cell is specialised to perform its function.
Axon- long structure which carries electrical impulses from the nerve cell down to the synapses
Myelin- insulating material which helps to speed up the transmission of the electrical impulses
Synapses- junctions which allow one nerve cell to pass impulses to other nerve cells
Dendrites- These increase the surface area, allowing other nerve cells to connect more easily
42
Describe how a muscle cell is specialised to perform its function.
Protein fibres- allow the cell to contract and relax
Lots of mitochondria- carry out respiration providing the energy required for muscle contraction
43
Describe how the root hair cell is specialised to perform its function.
Root hair- increases surface area of the cell, allowing it to absorb water and minerals more effectively
Large vacuole- speeds up the movement of water
Lots of mitochondria- carry out respiration providing the energy needed to transfer water and mineral ions
44
Why does a root hair cell not have chloroplasts?
-Chloroplasts use light energy to carry out photosynthesis. Root hair cells are found underground where there is no light.
-This means that root hair cells do not need to have chloroplasts.
45
Describe how xylem are specialised to perform their function.
Thick walls containing lignin- provide support to the plant and withstand pressure of water
No end walls between cells- xylem cells form a long hollow tube allowing water and minerals to flow more easily
No internal structures e.g. nucleus- makes it easier for water to travel through the xylem
46
Describe how phloem cells are specialised to perform their function.
Phloem transport dissolved sugars up and down the plant stem.
Cell walls between cells form sieve plates- allow dissolved sugars to pass easily through the phloem
Supported by companion cell- transfer energy needed to move dissolved sugars up and down the phloem
47
Describe how photosynthetic cells are specialised to perform their function.
Chloroplast- absorb light for photosynthesis
Placed in outer layers of stem and leaves- absorb more light
Large vacuole- keep plant rigid
Spread the leaf out- increases surface area to absorb more light
48
What is a stem cell?
A stem cell is an undifferentiated cell which can give rise to more cells of the same type and can differentiate to form other types of cells
Stem cells can produce more stem cells by mitosis and can also differentiate into specialised cells. They can be used to replace cells which have been damaged or destroyed
-e.g.in cases of brain or spine injury which can lead to paralysis
49
Describe the Use of Stem cells in a Bone Marrow Transplant
-Cancer of the bone marrow is called leukaemia. This is treated with a bone marrow transplant.
-First, radiation is used to destroy the patient's existing bone marrow. Bone marrow from a live donor is then transplanted into the patient.
-The donated stem cells now undergo mitosis, forming new bone marrow as well as differentiating to form new blood cells.
-We need to use a compatible donor to prevent the white blood cells from attacking the patient's body.
-Donated bone marrow also carries the risk of infecting the patient with viruses.
50
What is the difference between an embryonic stem cell and an adult stem cell?
-If cells are removed from the embryo they will differentiate into any cell type.
-Some stem cells remain in the bodies of adults. Adult stem cells are found in limited numbers at certain locations in the body.
-Adult stem cells can differentiate into related cell types only, for example, bone marrow cells can differentiate into blood cells and cells of the immune system but not other cell types (can be used for blood cell cancer)
51
Give the advantages and disadvantages of using embryonic stem cells for a transplant.
Advantages:
-can differentiate into a wide range of cell
Disadvantages:
-Some people think they are ethically unsuitable
-your body might reject them
-finding the right cells might be difficult
52
Give the advantages and disadvantages of using adult stem cells from a donor for a transplant.
Advantages:
-Can be found easily
Disadvantages:
-can only turn into certain cells
-your body might reject them
53
Give the advantages and disadvantages of using stem cell from yourself for a transplant.
Advantages:
-Won't be rejected
-Lots of them
Disadvantages:
-Use cells with a potentially bad gene/cell
54
What is therapeutic cloning?
-Therapeutic cloning could produce stem cells with the same genetic make-up as the patient.
-The technique involves the transfer of the nucleus from a cell of the patient, to an egg cell whose nucleus has been removed.
55
Describe the process of therapeutic cloning.
-Remove the nucleus from an egg cell
-Add a nucleus from the patient to the egg cell
-An electric shock is used to make the egg cell start
-The embryo made will have the same DNA as the patient
-Therefore, the embryo won't be rejected
-The stem cells from the embryo can be injected back into the body and from there it can replicated
-This can be used to cure diseases
56
Explain an advantage of therapeutic cloning.
-If any cell or tissue is transplanted into your body, then it is likely that the immune system will recognise that it is foreign.
-However, stem cells produced by therapeutic cloning have he same genes as the patient. This means that the patient's immune system will not see these stem cells as foreign and will not reject them.
57
Explain why some people will object to using stem cells produced by therapeutic cloning.
This is due to religious/ ethical issues. This is because some may reject the idea of embryos being created solely to provide cells for another person since the embryo is destroyed once the stem cells have been extracted.
58
Describe how stem cells work in plants.
-Cell division in plants occurs in regions called
meristems
-Cells of the meristem can differentiate to produce all types of plant cells at any time during the life of the plant.
-The main meristems are close to the tip of the shoot, and the tip of the root.
-In a growing shoot, new cells are being produced continuously near the tip. As the cells become older, further away from the tip, they become differentiated – they enlarge and develop vacuoles
59
State one way that plant stem cells from meristem tissue are different from adult stem cells in humans.
Plant stem cells can differentiate into any type of plant tissue. Adult stem cells in humans cannot do this. They can only differentiate into a narrow range of cells.
60
Give two uses of plant meristem tissue.
-Can produce crop plants for farmers such as plants which are resistant to diseases
-Can produce clones of plants quickly and cheaply which can be used to prevent a rare plant from going extinct
61
Describe how plant cloning works.
-Cells from meristems can be cloned. Meristematic cells are removed from a plant and grown in tissue culture
-The cells are grown in a culture medium that contains agar to provide support and water for the growing cells – along with nutrients and plant hormones to stimulate growth and cell division.
62
What is diffusion?
-Diffusion is the spreading out of particles resulting in a net movement of particles from an area of high concentration to an area of low concentration.
-No energy is needed for diffusion
63
Describe the factors which affect the rate of diffusion.
Concentration gradient- the greater the difference in concentration, the quicker the rate of diffusion.
Temperature- the higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly increasing the rate of diffusion.
Surface area- The greater the surface area to volume ratio, the faster the rate of diffusion.
64
Explain why is the concentration of carbon dioxide is greater inside of the cell
-The concentration of carbon dioxide inside the cell is high because carbon dioxide is constantly produced by aerobic respiration.
-The concentration of carbon dioxide outside the cell is low because it is constantly being removed by the bloodstream.
65
Explain why is the concentration of oxygen is greater outside of the cell
-The concentration of oxygen inside the cell is low because oxygen is used in the mitochondria for
aerobic respiration.
-The concentration of oxygen outside the cell is high because fresh oxygen is constantly being delivered to the cells by the red blood cells travelling in the bloodstream.
66
Describe what happens to urea produced by cells.
Urea diffuses out of cells into the blood plasma.
-That's because urea is in a higher concentration in the cells than in the plasma.
-The urea is then carried to the kidneys, where it is excreted.
67
Explain how fish get oxygen into their cells
-Fish take water into their mouth. This water contains dissolved oxygen.
-The water then passes through the gills where the oxygen diffuses into the bloodstream.
-The gills are covered with a large number of fine filaments where gases can pass in and out of the blood
68
Describe ways in which the filaments in fish increase the rate of diffusion
-Firstly, they present a very large surface area for gas exchange.
-Secondly, the thin membrane makes the diffusion distance short.
-Lastly, the efficient blood supply rapidly carries the oxygenated blood away.
-This ensures that the diffusion gradient is always high. All of these factors increase the rate of diffusion.
69
What is osmosis
Osmosis is the movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane.
70
What is a hypertonic, isotonic and hypotonic solution?
Hypertonic- a solution with a higher concentration of salt than normal body cells. Water leaves the cell by osmosis.
Isotonic- a solution with the same concentration of salt as a normal body cell. The movement of water in and out of the cell is constant.
Hypotonic- a solution with a lower concentration of salt than normal body cells. Water enters the cell by osmosis.
71
Describe the effects of osmosis on an animal cell
Hypertonic- the cell will shrivel
Isotonic- normal cell
Hypotonic- the cell will burst
72
Describe the effects of osmosis on a plant cell.
Hypertonic-the cell membrane shrinks away from the cell wall and the plant will die
Isotonic- the plant will wilt
Hypotonic- normal cell: plant swells but the cell wall is strong so holds the cell in place
73
Describe a method for the osmosis required practical.
-Prepare a range of sugar solutions. Measure 10 centimetres cubed of each solution and pour them into a series of boiling tubes. Label the boiling tubes with the concentration of the solution in it.
-Collect five potato cylinders and peel them. Use a cork borer to produce cylinders of potato. Use a scalpel to cut them to the same length. Record the size.
-Place each piece of potato into separate boiling tubes and leave for 24 hours.
-Remove the potato pieces from the solutions and dab off any excess solution using a paper towel.
-Measure the pieces of potato again and record the results.
74
What is the advantage of using a cork borer to produce potato cylinders in the osmosis practical
-When we use a cork borer, this produces potato cylinders all of the same diameter.
-This is important as the diameter of the potato cylinder could affect the rate of osmosis.
75
Why is the peel removed in the osmosis practical
-The skin on a potato may interfere with osmosis, preventing water from moving in or out of the tissue inside the potato.
-Therefore it is important that we peel the potato before we start.
76
What is the Advantage of Leaving the Cylinders Overnight rather than for an Hour in the Osmosis Practical
-In this practical, osmosis will cause water to move in or out of the potato cylinders (depending on the concentration of sugar solution that the cylinders are in).
-Osmosis takes time to happen. If we left the cylinders in the solution for only one hour, then this would not be enough time for osmosis to fully take place.
-Because of this, the potato cylinders might not change their mass / length enough to measure. This is why we leave them in the sugar solution overnight.
77
Why is it Important not to Press on the Cylinders in the Osmosis Practical
-When we take the potato cylinders out of the sugar solution, the cylinders will be wet. If we weighed them at this stage, then their masses would include the water on the surface.
To remove this, we gently roll the cylinders across paper towel.
-However, if we pressed on the potato cylinders, then we could force water out of the potato cells and this would give us inaccurate mass changes
78
What is the calculation for percentage change?
Percentage change= (change in mass/ original mass) x100
79
What is the advantage of looking at percentage change in mass rather than simply mass
Percentage change in mass takes into account the different start masses of the potato cylinders.
80
What is active transport.
Active transport is the movement of particles from an area of low concentration to an area of high concentration.
-(Against the concentration gradient).
-Energy is needed for active transport
81
Explain why glucose cannot move into the cell by diffusion
In diffusion, particles move down the concentration gradient.
-Glucose cannot move into the cell by diffusion as there is a higher concentration of sugars inside the cell than outside.
82
Explain why the cells lining the small intestines contain a large number of mitochondria
-Sugars move into the cell by active transport which requires energy from respiration.
-This means that the cells contain a large number of mitochondria as mitochondria are the parts of the cell where aerobic respiration takes place.
83
Explain why magnesium ions in root hair cells cannot be absorbed by diffusion
-The concentration of magnesium ions in the soil is less than the concentration inside the cell.
-This means that the ions cannot move by diffusion into the cell as diffusion is from a high concentration to
a lower concentration.
-Magnesium is needed to make chlorophyll for photosynthesis.
84
Why is active transport an advantage?
Active transport is an advantage because it allows an organism to take in nutrients that diffusion can't
85
Describe what happens to an organisms surface are to volume ratio as it gets larger.
As organisms get larger, their surface area to volume ratio falls sharply . This means diffusion becomes slower.
86
How does surface are to volume ration affect amoeba
-Amoeba are single-celled organisms.
-This means they have a large surface area : volume ratio
-Therefore, they can rely on diffusion to transport molecules in and out of the cell.
87
How does surface area to volume ration affect multicellular organisms
-Multicellular organisms have a very small surface area : volume ratio.
-This means that a large number of the organism's cells are not on the surface.
-Therefore, they cannot rely on diffusion alone to get the oxygen gas that they need for respiration.
88
Describe ways in which multicellular organisms solve the problem of getting oxygen to their cells efficiently.
-Have mechanisms to increase surface area proportionately and specialised cells for gas exchange, such as additional absorbing areas or adaptations of shape.
-Have a specialised transport system to carry oxygen directly to cells and keep distances to a minimum for diffusion.
89
Describe how the alveoli are specialised as exchange surfaces.
-Large surface area to volume ratio to maximise diffusion
-Thin walls (one cell thick) to reduce the distance gases have to travel which speeds up diffusion
-Lots of capillaries to provide a large blood supply and make it easier for gases to diffuse in and out
90
Describe how the intestines are specialised as exchange surfaces.
-Villi increase the surface area to maximise diffusion and active transport
-Single layer of thin cells to reduce the distance gases and minerals have to travel which speeds up diffusion and active transport
-Next to blood stream to transport food molecules easily
91
Explain how root hair cells are adapted as exchange surfaces.
-Root hairs increase the surface area to maximise osmosis and active transport
-Root hair penetrates between soil particles reducing the distance ions and minerals have to move
-Lots of mitochondria to release energy needed for active transport.
92
Explain how plant leaves are adapted as exchange surfaces.
-Large surface area to maximise the absorption of light and carbon dioxide
-Stomata open to allow diffusion of gases in and out
-Thin to minimise the distance gases need to travel
93
Compare diffusion, osmosis and active transport.
Diffusion:
-Substances move from a high to a low concentration down a concentration gradient
-Moves Carbon dioxide, oxygen, water, food substances, wastes
-Does not require energy
Osmosis:
-Water moves from a high to low concentration across a semi-permeable membrane and down a concentration gradient
-Moves water
-Does not require energy
Active Transport:
-Substances move against a concentration gradient
-Moves mineral ions into plant roots, glucose from the gut into intestinal cells, from where it moves into the blood
-Does require energy
94
What is binary fission?
Binary fission is the process of one bacterium splitting into two.
95
Describe the process of binary fission
-Circular DNA and plasmids replicate
-The cell gets bigger and circular DNA moves to opposite ends of the cell
-Cytoplasm begins to divide and new cell walls begin to form
-Cytoplasm divides and two daughter cells are produced
-Each has one copy of circular DNA but a variable number of copies of the plasmids
96
What affects the rate of binary fission?
Temperature- a decrease in temperature would cause enzymes in the bacteria to work at a slower rate
Nutrients- a decrease in the amount of nutrients would mean the bacteria are unable to build new molecules and generate the energy needed for binary fission
97
Describe a method for the growing germs practical
-Clean the bench with disinfectant to kill any microorganisms that could contaminate the culture
-Open a sterile agar gel plate near a Bunsen burner flame. The flame kills bacteria in the air
-Sterilise an inoculating loop by passing it through a Bunsen burner flame and use it to spread the chosen bacteria over the petri dish
-Place sterile filter paper discs containing the different antimicrobial agents onto the dish
-Place the dish in up side down in an incubator at 25 degrees Celsius and leave for 24 hours
-After 24 hours, observe and measure the inhabitation zones caused by the antimicrobial agents and work out which was most effective
98
Explain why the lid is loosely secured with tape.
Securing the lid prevents unwanted bacteria from entering the dish. However, it is loosely secured so that oxygen is able to enter which prevents the growth of harmful microbes.
99
Explain why the dishes are stored upside down.
The dishes are stored upside down because during the incubation period, water droplets can form inside the lid.
-If the dishes were placed right way up, they can drop onto the agar gel which would prevent the bacteria from growing.
-By storing upside down, we prevent water dropping on the bacteria and the dishes from becoming contaminated
100
Explain why the temperature for incubation is set to 25 degrees Celsius in schools.
The dishes are incubated at 25 degrees Celsius in schools because this reduces the risk of pathogenic microorganisms from growing.
