1 - Key Concept in Biology

Question 1

Is a plant cell a prokaryotic cell or a eukaryotic cell?

Answer 1

A eukaryotic cell

Question 2

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

Answer 2

Mitochondria

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

False

Electron microscopes have both a higher resolution and a higher magnification than light microscopes.

Question 6

How has electron microscopy increased biologists’ understanding of cells?

Answer 6

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

Question 7

A specimen is 100 μm wide. Calculate the width of the image of the specimen under a magnification of x200
Give your answer in mm
Use the equation: magnification = image size/real size

Answer 7

20mm
Image size = magnification x real size
= 200 x 100 μm = 20000μm
=20000μm / 1000 = 20mm

Question 8

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

Answer 8

root hair cells

Question 9

What is the function of a sperm cell?

Answer 9

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

Question 10

What is the function of xylem cells? How are xylem cells specialised for this function?

Answer 10

Xylem cells function to transport water and minerals up plants. They are specialised for their function because the cells are long and are joined end to end, forming hollow tubes. This means that substances can flow through them.

Question 11

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

Answer 11

A nerve cell carries electrical impulses 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.

Question 12

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

Answer 12

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

Question 13

Name a gas molecule that can diffuse through cell membranes.

Answer 13

E.g. oxygen and carbon dioxide

Question 14

How does the concentration gradient affect the rate of diffusion?

Answer 14

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

Question 15

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.

Answer 15

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, meaning there will be a greater concentration gradient and so a faster rate of diffusion

Question 16

What type of membrane is needed for osmosis to happen?

Answer 16

A partially permeable membrane

Question 17

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

Answer 17

False.

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

Question 18

Lois has two potato cylinders. The fluid inside the potato cell has a concentration of 0.3 mol/dm^3. She weighs the two cylinders and places one into a beaker of pure water and the other into a beaker of 0.1 mol/dm^3 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.

Answer 18

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 to an area of lower water concentration. 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 to an area of lower water concentration

Question 19

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

Answer 19

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, causing the plant to lose water and wilt.

Question 20

What is active transport?

Answer 20

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

Question 21

Give one difference between active transport and osmosis

Answer 21

Active transport needs energy
Osmosis is used to move water only
Active transport moves substances from a lower concentration to a higher concentration, whereas osmosis moves water from a higher to a lower water concentration

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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 bloodstream.

Question 24

How do enzymes affect the rate of a reaction?

Answer 24

Enzymes increase the rate of a reaction

Question 25

What is an active site of an enzyme?

Answer 25

The active site is part of the enzyme that the substrate fits into

Question 26

Give two variables that affect the rate of an enzyme-controlled reaction

Answer 26

Temperature and pH

Question 27

What is the ‘lock and key’ model of enzyme action?

Answer 27

The ‘lock and key’ model is a simplified model of enzyme action. It states that a reaction will only be catalysed if the shape of the substrate exactly matches the shape of the enzyme’s active site, so that the substrate fits directly into the active site

Question 28

A student is investigating the effect in pH on the rate of amylase activity. Suggest how the student could control the temperature of the amylase and starch solution during the experiment.

Answer 28

The student could use an electric water bath. Alternatively, the student could put a test tube containing the solution in a beaker of water over a Bunsen burner and use a thermometer to help keep the water at a constant temperature

Question 29

A scientist carried out an enzyme-controlled reaction. After 100 seconds, 45 cm^3 of the product had been produced. Calculate the rate of reaction, cm^3/s. Use the equation: rate of reaction = amount of product formed / time

Answer 29

Rate of reaction = amount of product formed / time = 45 / 100 = 0.45 cm^3

Question 30

Which type of molecule is broken down into amino acids?

Answer 30

Proteins are broken down into amino acids

Question 31

What are the products of lipid digestion?

Answer 31

glycerol and fatty acids

Question 32

In which organs are proteases produced?

Answer 32

The stomach, the pancreas and the small intestine

Question 33

Which organ produces bile and where is bile stored?

Answer 33

The liver produces bile. It’s stored in the gall bladder

Question 34

Vikesh is eating rice, which is a starchy food. Name the enzyme that will break down this starch during digestion. Which parts of Vikesh’s body produces this enzyme?

Answer 34

The starch will be broken down by amylase. Amylase is produced in the salivary glands, the pancreas and the small intestine.

Question 35

What does the body use the products of digestion for?

Answer 35

E.g. the products of digestion can be used to build new carbohydrates, proteins and lipids, and some of the glucose produced is used in respiration

Question 36

Give two functions of bile and explain how these aid digestion.

Answer 36

Bile neutralises hydrochloric acid, making conditions in the small intestine alkaline. Enzymes in the small intestine work best in alkaline conditions. Bile also emulsifies fats. This means it breaks fat down into tiny droplets, which gives lipase enzymes a much bigger surface area to work on during digestion. These two effects of bile both increase the rate of digestion.