TOPIC 1 - CELL BIOLOGY

Question 1

What are eukaryotic cells?

Answer 1

They are complex and include animal and plant cells.

Question 2

What are prokaryotic cells?

Answer 2

They are smaller and simpler eg bacteria.

Question 3

What is the nucleus?

Answer 3

Contains genetic material that controls activities of the cell.

Question 4

What is cytoplasm?

Answer 4

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

Question 5

What is the cell membrane?

Answer 5

Controls what goes in and out of the cell.

Question 6

What are mitochondria?

Answer 6

These are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work.

Question 7

What are ribosomes?

Answer 7

These are where proteins are made in the cell.

Question 8

What is the cell wall (plant cell)?

Answer 8

Made of cellulose. It supports and strengthens the cell.

Question 9

What is the vacuole (plant cell)?

Answer 9

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

Question 10

What are the chloroplasts (plant cell)?

Answer 10

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

Question 11

Explain bacteria cells.

Answer 11

They are prokaryotes.
They don’t have chloroplasts or mitochondria.
They have :cytoplasm, cell membrane, cell wall, one or more small rings of DNA called plasmids.
They don’t have a true nucleus, instead they have a single circular strand of DNA that floats freely in the cytoplasm.

Question 12

What is the formula to calculate magnification?

Answer 12

Magnification = image size/real size

Question 13

How do you prepare a microscope slide?

Answer 13

Add a drop of water to the middle of a clean slide.
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.
Using the tweezers, place the epidermal tissue into the water on the slide.
Add a drop of iodine solution. This is a stain which is used to highlight objects in a cell by adding colour to them.
Place a cover slip on top. To do this, stand the cover slip up right 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 as they will obstruct your view of the specimen.

Question 14

How do you use a light specimen?

Answer 14

Clip the slide you have prepared onto the stage.
Select the lowest powered objective lenses (the one that produces the lowest magnification).
Use the coarse adjustment knob to move the stage up to just below the objective lens.
Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus.
Adjust the focus with the fine adjustment knob, until you get a clear image of what is on the slide.
If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.

Question 15

What is cell differentiation?

Answer 15

Differentiation is the process by which a cell changes to become specialised for its job. As cells change, they develop different sub cellular structures and turn into different types of cells. This allows them to carry out specific functions.

Question 16

Name five specialised cells.

Answer 16

Sperm cells 
Nerve cells 
Muscle cells 
Root hair cells 
Phloem and Xylem cells

Question 17

Explain sperm cells.

Answer 17

They are specialised for reproduction.
It’s function. Is to get the male DNA to the female DNA. It has a long tail and a streamlined head to help it swim to the egg. There are lots of mitochondria in the cell to provide the energy needed. It also carries enzymes in its head to digest through the egg cell membrane.

Question 18

Explain nerve cells.

Answer 18

They are specialised for rapid signalling.
They carry electrical signals from one part of the body to another. They are long (to cover more distance) and have branched connections at their ends to connect to other nerve cells and form a network throughout the body.

Question 19

Explain muscle cells.

Answer 19

They are specialised for contraction.
Their function is to contract quickly. They are long (so they have space to contract) and contain lots of mitochondria to generate energy needed for contraction.

Question 20

Explain root hair cells.

Answer 20

They are specialised for absorbing minerals and water.
They are on the surface of plant roots, which grow into long “hairs” that stick out into the soil. This gives the plant a big surface area for absorbing water and mineral ions from the soil.

Question 21

Explain phloem and xylem cells.

Answer 21

They are specialised for transporting substances.
These cells form tubes, which transport substances such as food and water around plants. To form the tubes, the cells are long and joined end to end. Xylem cells are hollow in the centre and the phloem cells have very few subcellular structures, so that stuff can flow through them.

Question 22

What are chromosomes?

Answer 22

They are found as genetic material in the nucleus.
They are coiled up lengths of DNA molecules.
Each chromosome carries a large number of genes. Different genes control the development of different characteristics.
Body cells usually have two copies of each chromosome - one from the mother and one from the father.
23 PAIRS OF CHROMOSOMES IN A HUMAN CELL.

Question 23

What is mitosis?

Answer 23

Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle.
The stage of the cell cycle when the cell divides is called mitosis.

Question 24

What are the three stages of the cell cycle?

Answer 24

1 - replication of DNA to form two copies of each chromosome and synthesis of new sub-cellular structures.
2- mitosis
3-cell divides in two.

Question 25

Explain the growth and DNA replication stage of the cell cycle.

Answer 25

The DNA is spread out on long strains in a cell that is not dividing.
Before it divides, the cell has to grow and I caress the amount of subcellular structures such as mitochondria and ribosomes.
It then duplicates its DNA - so there is one copy for each new cell. The DNA is copied and forms x-shaped chromosomes. Each ‘arm’ of the chromosome is a exact duplicate of the other.

Question 26

Explain the mitosis stage of the cell cycle.

Answer 26

The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms on each chromosome go to opposite ends of the cell.
Membranes form around each of the sets of chromosomes. These become the nucleus of the two new cells - the nucleus has divided.
The cytoplasm and cell membrane then divide.
The cell has produced two new daughter cells. The daughter cells contain exactly the same DNA - they are identical to the parent cell.

Question 27

What is binary fission?

Answer 27

Prokaryotic cells can reproduce through binary fission. The cell splits in two.
The circular DNA and plasmids replicate.
The cell gets bigger and the circular DNA strands move to opposite poles of the cell.
The cytoplasm begins to divide and new cell walls begin to form.
The cytoplasm divides and two daughter cells are produced. Each daughter cells has one cope of the circular DNA, but can have variable number of copies of plasmids.

Question 28

How can you grow bacteria in the lab? (Practical).

Answer 28

Bacteria can be grown in a culture medium which contains carbohydrates, minerals, proteins and vitamins they need to grow.
The culture medium can be a nutrient broth solution or solid agar jelly.
Bacteria grown on agar plates will form visible colonies on the surface of the jelly or will spread out to give an even covering of bacteria.
(To make an agar plate, hot agar jelly is poured into shallow round plastic dishes called Petri dishes. When the jelly has cooled and set, inoculating 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)
At schools, cultures are not to be kept above 25 degrees Celsius because harmful pathogens are more likely to grow above this temperature. In industrial conditions, cultures are incubated at higher temperatures so that they can force a lot faster.

Question 29

How can you investigate the feat of antibiotics on bacterial growth? (Practical)

Answer 29

You can test the action of antibodies or antiseptics on cultures of bacteria.
Place paper discs soaked in different types (or different concentrations) of antibodies on an agar plate that has an even covering of bacteria. Leave some space between the discs.
The antibiotic should diffuse into the agar jelly. Antibiotic resistant bacteria will continue to grow on the agar around the paper discs. However, non-resistant strains will die. A clear area will be left where bacteria have died - this is called the inhibition zone.
Make sure to use a control - this is a paper disc that has not been soaked in antibiotic. Instead, soak it in steeple water. This will ensure that any difference between growth of the bacteria around the control disc and around one of the antibiotic disc is due to the affect of antibiotic alone.
Leave the plate for 48 hours at 25 degrees celsius.
The more effective the antibiotic is against the bacteria, the ,after the zone of inhibition.

Question 30

How can you ensure you use uncontaminated cultures while culturing bacteria?

Answer 30

The Petri dishes and culture medium must be sterilised before use, eg by heating to a high temperature, to kill any unwanted microorganisms that may be lurking on them.
If an inoculating loops is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame.
The lid of the Petri dish should be lightly taped on to stop microorganisms from the air getting it (after the bacteria has been transferred)
The Petri dish should be stores upside down - to stop drops of condensation falling onto the agar surface.

Question 31

What are embryonic stem cells?

Answer 31

Embryonic stem cells can turn into any type of cell.
Stem cells are undifferentiated, they can produce lots more undifferentiated cells. They can differentiate into different types of cells, depending on what instructions they are given.
They are found in early human embryos.

Adults also have stem cells, but they’re only found in certain places, like bone marrow. However, these can’t turn into any cell type, only certain ones such as blood cells.

Question 32

How can stem cells be used to cure many diseases?

Answer 32

Stem cells can be transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient who receives them.
Embryonic stem cells could be used to replace faulty cells in sick people. - you could make insulin producing cells for people with diabetes or nerve cells for people paralysed by spinal injuries.
You could prevent the cell from being rejected from the patients body by therapeutic cloning - the embryo could be made to have the same genetic information as the patient.

Question 33

Why are some people against stem cell research?

Answer 33

They feel embryos should t be used for experiments since they have potential of human life.

Question 34

How can stem cells be used to produce identical plants?

Answer 34

In plants stem cells are found in the meristems (parts of the plant where growth occurs).
Throughout the plants entire life, cells in the meristem tissues can differentiate into any type of plant cell.
These stem cells can be used to produce clones of whole plants quickly and cheaply.
They can be used to grow more plants of rare species.
Stem cells can also be used to grow crops of identical plants that have desired features for farmers, eg disease resistance.

Question 35

What is diffusion?

Answer 35

The gradual movement/spreading out of particles from areas of higher concentration to lower concentration.
The bigger the concentration gradient, the faster the diffusion rates.
A higher temperature will also give a faster diffusion rate because the particles have more energy, so move around faster.

Question 36

What is osmosis?

Answer 36

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

Water molecules pass both ways through the membrane because the water molecules move about randomly all the time.
There is a steady net flow because there will be more water molecules on one side than the other. (Into the region with fewer water molecules/the stronger sugar solution)
This means the string sugar solution gets more dilute. The water acts as if it is trying to “even up” the concentration either side of the membrane.

Question 37

What is the practical to observe the effect of sugar solutions on plant tissue?

Answer 37

Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them. One should be pure water and another should be a very concentrated sugar solution. Then you should have a few others with concentrations in between.
Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours.
When you take them out, dry them and measure their masses again.
If the cylinders have drawn in water by osmosis, they will have increases in mass.
The dependent variable is the chip mass and the independent variable is the concentration of the sugar solution. All other variables must be kept the same to ensure the test is fair.

Question 38

What is active transport?

Answer 38

When substances are absorbed against a concentration gradient.
Allows an object to absorb minerals from a very dilute solution, against a concentration gradient. It needs energy from respiration to make it work.

Question 39

How do root hairs take in minerals and water?

Answer 39

Each branch of a root will be covered in millions of microscopic ‘hairs’.
This gives the plant a large surface area for absorbing water and mineral ions for healthy growth.
The concentration of minerals is usually higher in the root hair cells than in the soil around them. So, they take in minerals using active transport.

Question 40

How is active transport used in our bodies?

Answer 40

It is used in the gut when there is a lower concentration of nutrients in the gut, it a higher concentration of nutrients in the blood.
Sometimes, the nutrients will diffuse naturally into the blood if there is a higher concentration of glucose and amino acids in the blood.
However, sometimes there is a lower concentration in the gut than in the blood. This means the concentration gradient is the wrong way.
So, active transport is used. This means that glucose can be taken into the blood when it’s concentration is already higher than in the gut.

Question 41

Why do multicellular organisms need exchange surfaces?

Answer 41

In single-called organisms, gases and dissolved substances can diffuse directly into (or out of) the cell across the cell membrane. This is because they have a large surface area compared to their volume.
However, multicellular organisms have a smaller surface areas compared to their volume which means not enough substances can diffuse from their outside surface to supply their entire volume this means they need an exchange surface for efficient diffusion. The exchange surface structures have to allow enough of the necessary substances to pass through.
Exchange surface are adapted to maximise effectiveness:
They have a thin membrane, so substances only have a short distance to diffuse.
They have a large surface area so logs of a substance can diffuse at once.
Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly
Has exchange surfaces in animals are often ventilated too - air moves in and out.

Question 42

How does gas exchange happen in the lungs?

Answer 42

Oxygen is transferred to the blood and waste carbon dioxide is removed from the blood.
Gas exchange takes place in little air sacks called alveoli.

Question 43

How are alveoli specialised to maximise diffusion?

Answer 43

A large surface area
Moist lining for dissolving gases
Very thin walls so there is a short diffusion distance
A good blood supply.

Question 44

How do the villi provide a large surface area in the small intestine?

Answer 44

The inside of the small intestine is covered in millions of tiny little projections called villi.
They increased the surface area so that digested food is absorbed more quickly into the blood.
They have:
A single layer of surface cells
A very good blood supply to assist quick absorption.

Question 45

How are leaves structured to ,eg gases diffuse in and out of cells?

Answer 45

Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens. The leafs structure is adapted so this can happen easily.
The underneath of the leaf is an exchange surface. It is covered in atoms which carbon dioxide diffuses in through.
Oxygen and water vapour diffuse out of the stomata.
The size of the stomata is controlled by guard cells. These close the stomata if the plant is losing water too quickly (quicker than the roots can replace it). Without the guard cells the plant would wilt.
The flattened shape of the leaf increases the area of this exchange so that it is more effective.
The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the area of this surface so there is more chance for carbon dioxide to get into the cells.

Question 46

How are fish adapted for gas exchange?

Answer 46

Their gills have a large surface area.
Water (containing oxygen) enters the fish through its mouth and passes out through the gills. As this happens oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water.
Each gill is made of lots of thin plates called gill filaments which give a big surface area for exchange of gases.
The gill filaments are covered in tiny structures called lamellae, which increases the surface area even more.
The also have a thin surface layer of cells in minimise the distance that the gases have to diffuse.
Blood flows through the lamellae in one direction and water flows over in the opposite direction. This maintains a large concentration gradient between the water and the blood.
The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.

Question 47

What is interphase?

Answer 47

Interphase

The cell grows and carries out its functions and makes copies of its DNA. The DNA replicates and forms chromatin.

Question 48

What is the first stage of cell division?

Answer 48

Prophase
When the chromatin coils and condenses to form chromosomes. The two chromatids are connected by a centromere. The nuclear membrane begins to disappear.

Question 49

What is the second stage of cell division?

Answer 49

Prometaphase.

The nuclear membrane disappears.

Question 50

What is the third stage of cell division?

Answer 50

Metaphase.

The chromosomes align in the middle of the cell.

Question 51

What is the fourth stage of cell division?

Answer 51

Anaphase.

The chromatids move to opposite sides of the cell.

Question 52

What is the final stage of cell division?

Answer 52

Telophase.
As the chromatids reach opposite ends of the cell, a new membrane beings to form around them. This results in two new daughter nuclei. Following telophase, the cell splits, a process known as cytokinesis.