CGP

Is a plant cell a prokaryotic cell or a eurakryotic cell?

Is a plant cell a prokaryotic cell or a eurakryotic cell?

a eukaryotic cell ( A eukaryotik cell is a complex cell, e.g. a plant or animal cell, whereas a prokaryotic cell is a small simple cell, e.g. a bacterium.)

In which sub-cellular structures do most of the reactions of aerobic respiration take place

mitochondria

Describe the main similarites and differences between a bacterial cell and plant cell.

Similarities: e.g. both have a cell membrane, a cell wall and a cytoplasm.

Differences: e.g. plant cells has chloroplasts and mitochondria but bacteria do not. Plant cells also have a true nucleus, whereas bacteria have a single circular strand of DNA that floats freely in the cytoplasm. Bacterial cells may also contain small rings of DNA called plasmids.

What is the function of the cell membrane, nucleus and cytoplasm?

• cell membrame. This holds the cell together and controls what enters and leaves.

• nucleus. This contains the genetic material that controls the activites of the cell.

• cytoplasm. This is a gel-like substance where chemical reactions happen. It contains enzymes that control tgese reactions.

What is the purpose of the fine adjustment knob on a light microscope?

It’s used to focus the lens until a clear image of what’s on the slide that appears.

True or false? Electron microscopes have a smalled magnification than light microscopes, but they have a higher resolution than light microscopes

False. Electron microscopes have both a higher resolution and a higher magnification than light microscopes. (Resolution is the ability to distinguish between two points. Magnification is the process of making something look bigger.

How has electron microscopy increased biologists’ understanding if cells?

Electron microscopes let us study cells in much finer detail than light microscopes. This has enables biologists to see and understand more sub-cellular structures, such as ribosomes and plasmids, and the internal structures of mitochondria and chloroplasts.

Troian uses a light microscope to study onion cells. The diagram on the right shows the slide that she prepared. Explain why Troain added a drop of iodine to the slide.

Iodine is a stain. Troian used it to highlight objects in the onion cells by adding colour to them, making them easier to see.

A specimen is 100 μm wide. Calculate the width of the image of the specimen under a magnification of x 200.

Give your answer in mm.

Use the equation: magnification=image size/real size

1. 20 mm. Image size = magnification x real size

   = 200 × 100 μm = 20 000 μm

   = 20 000 μm ÷ 1000 = 20mm

Which cells in plants are specialised for absorbing water and minerals from the soil?

root hair cells ( They’re found on the surface of plant roots.)

What is the function of a sperm cell?

To transport the male DNA to the female DNA in eggs for reproduction.

How does the ability to differentiate differ between plant cells and animal cells?

The ability to differentiate is lost at an early stage in most animal cells (after they have become specialised), but lots of plants cells don’t ever lose this ability.

What is the function of xylem cells?

Xylem cells function to transport water and minerals up plants. They are specialised for their function because the cells are song and are joined end to end, forming hollow tubes.

How are xylem cells specialised for this function?

This means that substances can flow through them.

What is the function of a nerve cell? How is a nerve cell adapted for its function?

A nerve cell carries electrical impulses (signals) from one part of the body to another.

The cell is long and has branched connections at its ends to connect to other nerve cells and form a network throughout the body. This allows for rapid signalling.

Exocrine acinar cells function to produce lots of digestive systems (proteins(, which are then secreted from the pancreas. Suggest one way that these cells may be specialised for their function.

E.g. the exocrine acinar cells may contain a large number of ribosomes for the synthesis of digestive enzymes.

In human body cells, are chromosomes normally found in pairs or triplets?

in pairs (one comes from the mother and one from the father)

Which of the following do chromosomes contain?

A. mitochondria B. cytoplasm C. genes D. amino acids

C (Chromosomes are coiled up lengths of DNA, which carry a large number of genes.)

What is mitosis? What is it used for?

Mitosis is the stage of the cell cycle when the cell divides. Organisms use mitosis to grow or replace cells that have been damaged.

A normal human body cell contains 23 pairs of chromosomes. How many chromosomes would be in each new human cell formed by mitosis?

Each cell will have 46 chromosomes (23 pairs).

True or false? Binary fission is when bacteria die due to unfavourable conditions.

False. Binary fission is a type of simple cell divison used by bacteria to multiply.

What is meant by the ‘mean division time’ of a bacterial cell?

The average amount of time it takes for one bacterial cell to divide into two.

A scientist starts to grow a colony of bacteria in nutrient broth under optimum conditions for bacterial divison. After a period of time, the nutrients in the broth are used up. How will this cause the number of bacteria in the colony to change?

The number of bacteria will stop increasing (they can no longer divide) and then the number will start to decline as the bacteria begin to die.

Under certain conditions, a bacterial cell has a mean divison time of 40 minutes. How many bacterial cells will it have produced after 200 minutes?

32 cells. Number of divisions = total time ÷ mean divison time

200 minutes ÷ 40 minutes = 5 divisions

so 2⁵ = 2 × 2 × 2 × 2 × 2 = 32 cells will be produced

Under certain conditions, a bacterial cell has a mean division time of 40 minutes. How many bacterial cells will it have produced after 2 hours?

64 cells. 2 hours x 60 = 120 minutes

Number of divisions = total time ÷ mean division time

120 minutes ÷ 20 minutes = 60 divisions

so 2⁶ = 2 × 2 × 2 × 2 × 2 × 2 = 64 cells will be produced.

Name the clear area that forms around a disc on an agar plate when bacteria die.

zone of inhibition zone

Why are cultures incubated at a maximum temperature of 25 °C in schools?

Harmful bacteria are more likely to grow above this temperature

Explain the aseptic techniques you would use when preparing an uncontaminated culture on an agar plate.

E.g. sterilise the Petri dish and culture medium before use by heating them to a high temperature. Sterilise the inoculating loop (used to transfer the bacteria onto the agar plate) by passing it through a hot flame. These first steps are taken to kill any unwanted microorganisms. After transferring the bacteria, the lid of the Petri dish shouldbe lightly taped on to stop microorganisms in the air getting in, and the Petri dish should be stored upside down to stop any condensation droplets from falling onto the agar surface.

What is a stem cell?

An undifferentiated cell which has the ability to become one of many different types of cell or stem cells.

Where can stem cells be found in an adult human? What do they do?

Bone marrow (and other places). They can turn into specific cells, such as blood cells.

What type of plant tissue contains stem cells?

meristem tissue (This is where growth occurs).

Describe a potential risk of stem cell therapy.

E.g. if stem cells contaminated with a virus, the virus could be passed onto the patient.

Josie has been warned that a plant disease could start to spread to crops on her farm in the near future. How could Josie use stem cells to ensure her crop yield is not affected by the disease?

Josie could use stem cells to grow crops of identical plants with disease resistance. The plantswould then be more likely to survive if the disease reaches her farm.

Heart attacks are caused by the blockage of coronary arteries that carry oxygen to the heart. This can result in damage or death of heart muscle. Suggest how embryonic stem cells could potentially be used to treat a patient after a heart attack.

Embryonic stem cells could be made to develop into heart muscle cells. These could repair the damaged tissure or replace the damaged cells after a heart attack.

Breifly outline the ethical arguements for and against embryoins stem cell therapy.

Some people think it’s wrong to take stem cells from embryos as they’re a human life. Others disagree and think it is unethical to let patients suffer when there is something we could potentially do to help.

Name a gas molecule that can diffuse through cell membranes.

e.g. oxygen and carbon dioxide

How does the concentraion gradient affect the rate of diffusion?

The bigger the concentration gradient, the faster the rate of diffusion.

Oxygen diffuses from the blood stream into muscles. During exercise, oxygen is used up in the muscles faster than when a person is at rest. Suggest how the rate of oxygen diffusion might differ when a person is running compared to when they are sitting down.

The diffusion rate will be greater when the person is running compared to when the person is sitting down. This is because there will be a lower concentration of oxygen in the muscles (as it is used up quicker), meaning there will be a greater concentration gradient and so a faster rate of diffusion.

What type of membrane is needed for osmosis to happen?

A partially permeable one (it has small holes in it, so only tiny molecules can pass through.)

True or false? Oxygen entering the blood from the lungs is an example of osmosis.

False. This happens by diffusion. Osmosis involves the movement of water.

Lois has two potato cylinders. The fluid inside the potato cells has a concentration of 0.3 mol/dm³. She weighs the two sylinders and places one into a beaker of pure water and the other into a beaker of 1.0 mol/dm³ glucose solution. After 24 hours, she removes the cylinders, dries them, and measures their final mass. Explain how the mass of each potato cylinder will have changed after 24 hours.

The mass of the cylinder in pure water will have increased because the water will have moved by osmosis from an area of higher water concentration (the pure water) to an area of lower water concentration (the potato). The mass of the cylinder in the glucose solution will have decreased, as water will have moved by osmosis from an area of higher water concentration (the potato) to an area of lower water concentration ( the glucose solution).

The potato cylinders weren’t dried properly during this experiment, so the excess water added to the mass of the potato. How could Lois reduce the effect of errors like this?

Lois could repeat the experiment and calculatea a mean percentage change in mass.

When plants lose water, they start to wilt. Explain why most plants will wilt if the soil they are growing on is flooded with salty sea water.

The sea water has a high concentration of salt, so the water concentration in the soil will be lower than that in the plant. This means water would move by osmosis from the plant to the soil (from a higher concentration to a lower concentration), causing the plant to lose water and wilt.

What is active transport?

The movement of substances from a lower concentration to a higher concentration using energy from respiration.

Give one difference between active transport and osmosis.

Differences include; e.g. active transport needs energy, whereas osmosis does not.

Active transport is useded to move many substances, whereas osmosis just moves water.

Active transport moves substances from a lower concentration to a higher concentration, whereas osmosis moves water from a higher to a lower water concentration.

The diagrams on the right represent the transport of substances across cell membranes. Which diagram, 1 or 2, shows active transport taking place? Explain your answer.

Diagram 1. The lions are moving from a lower concentration to a higher concentration.

Explain why root hair cells need to use active transport to take in minerals

The concentration of minerals is usually higher in the root hair cells than in the soil, so root hair cells can’t absorb minerals using diffusion (minerals would diffuse out of the root hair cells).

In humans, glucose is absorbed into the bloodstream from the gut. Why is active transport important for this process?

Sometimes the concentration of glucose in the gut is lower than the concentration of glucose in the blood, so cells must use active transport to absorb glucose into the bloodstream.

How does size of an organism affect its surface area to volume ratio?

The larger an organism is, the smaller its surface area to volume ratio.

True or false? Single-celled organisms with a large surface area to volume ratio can easily exchange substances with the enviroment, without adaptations.

True. Enough substances can be exchanged across their cell membrane to supply the needs of the cell.

Outline the transport of gases in and out of cells in gas exchange.

How are the gas exchange surfaces of an elephant adapted to maximise effectiveness?

A tiny elephant can be represented by a 3cm x 3cm x 3cm block. Calculate the surface area to volme ration of the elephant.