Cells & Enzymes

Question 1

Describe the properties of the cell membrane.

Answer 1

• thin& elastic- has tiny pores
• selectively permeable
• controls the movement of substances in and out of a cell

Question 2

Describe the properties of the cytoplasm.

Answer 2

• jelly-like and contains mainly water
• contains many small structures called organelles
• where most chemical reactions take place

Question 3

Describe the properties of the nucleus.

Answer 3

• largest organelle in the cell
• not present in red blood cell
• controls the activities of the cell
• contains chromosomes

Question 4

Describe the properties of the mitochondrion.

Answer 4

• involved in the release of energy in respiration

Question 5

Describe the properties of the cell wall.

Answer 5

• found outside the cell membrane
• thick and tough
• made of cellulose
• contains large holes
• freely permeable
• keeps the shape of the cell and protects inner structures

Question 6

Describe the properties of the vacuole.

Answer 6

• large, central space filled with cell sap
• storage of various substances
  -might be found in animal cells as well, although would be much smaller

Question 7

Describe the properties of the choroplast.

Answer 7

• contains a green pigment called chlorophyll
• absorbs light energy in photosynthesis for making food

Question 8

Describe the properties of the ribosome.

Answer 8

• tiny structures in the cytoplasm
• site of protein synthesis

Question 9

State the 6 differences between an animal cell and a plant cell.

Answer 9

• animal cell is relatively smaller in size, while the plant cell is larger in size
• animal cell is irregularly shaped, whole a plant cell is regularly shaped (cell membrane/ cell wall)
  -animal cell has no cell wall, plant cells have cell walls
• the vacuole is small or absent, nucleus is at the center in an animal cell, while in a plant cell, there is a large central vacuole and the nucleus is near the cell wall.
• glycogen granule as food storage in an animal cell, starch as food storage in a plant cell
• animal cells have no chloroplast, plant cells have chloroplast

Question 10

Name a cell.

Answer 10

Stomach or muscle cell

Question 11

Name a tissue.

Answer 11

Stomach wall tissue

Question 12

Name an organ.

Answer 12

Stomach

Question 13

Name an organ system.

Answer 13

Digestive system.

Question 14

Name an organism.

Answer 14

Human.

Question 15

List the similarities of an animal cell and a plant cell.

Answer 15

• both have a cell membrane surrounding the system
• both have a nucleus
• both contain mitochondria

Question 16

List the levels of organization.

Answer 16

Cell, tissue, organ, organ system, organism

Question 17

What is the cell theory?

Answer 17

• all organisms are composed of one or more cells
• the cell is the basic unit of organization of organisms
• all the cells come from pre-existing cells

Question 18

Describe metabolism.

Answer 18

Metabolism is…
- all the chemical reactions taking place inside a body cell
- either catabolic or anabolic

Question 19

What is catabolism?

Answer 19

It is the breaking down of of complex molecules into simpler ones.

Question 20

What is anabolism?

Answer 20

It is the building up of complex molecules from simpler ones.

Question 21

What is a catalyst?

Answer 21

It is a substance that increases the rate of a chemical reaction and is not changes by the reaction.

Question 22

What is an enzyme?

Answer 22

It is a protein that functions as a biological catalyst speeding up chemical reactions in an organism.

Question 23

What are the seven properties of enzymes?

Answer 23

• proteins in nature
• speed up biochemical reactions
• remains unchanged at the end pf the reaction and can be reused.
• are effective in small quantities
• reactions they catalyse are reversible
• are highly specific. one enzyme can catalyse only one stype of reaction
• affected by temperature and pH. They work efficiently within a particular range of temperature and pH.

Question 24

Why do we need enzymes?

Answer 24

It is because the metabolism inside organisms is low. Without catalysts, most of the reactions that happen in cells would be far too low to allow life to go on. Enzymes biocatalysts are needed for the reaction to start.

Question 25

What is a substrate?

Answer 25

It is the molecule an enzyme works on.

Question 26

What is an active site?

Answer 26

It is the small area where the substrate binds to the enzyme. It is of a particular 3-D shape which must match the shapes of specific substrates for the reaction to take place.

Question 27

What can the specificity of the enzymatic reaction be explained by?

Answer 27

The lock-and-key model.

Question 28

Explain the reaction of the substrate when paired with an active site.

Answer 28

Enzyme + Substrate = Enzyme-substrate complex = Product + Enzyme

Question 29

What will happen if the shape of an active site of an enzyme molecule is changed?

Answer 29

The substrate cannot fit into the active site of the enzyme molecule. The enzyme molecule will not catalyse the reaction anymore.

Question 30

What are the factors affecting enzyme activity?

Answer 30

• temperature
• pH
• substrate concentration
• enzyme concentration

Question 31

How does temperature affect enzyme activity? (explain thoroughly)

Answer 31

At 0 degrees, the enzymes are inactivated. The reaction rate is low due to the slow movement of substrates. Rate of reaction increases again as temperature rises. Between 10-40 degrees, rate of enzymatic reaction increases as temperature increases. This is because substrates move faster at higher temperature. Hence there are increasing chances for them to collide with an active site of an enzyme to form the enzyme- substrate complex. Thus products are formed at a higher rate.

At around 40 degrees, enzymatic reaction occurs most rapidly. In this case 40 degrees is called the optimum temperature for the enzyme.

> 40 degrees, the reaction rate drops rapidly and stops at around 60 degrees. At high temperature, bondings within the enzyme are broken. Hence, the shapes of active sites are changed. Enzymes lose their catalytic function and are said to be denatured.

Question 32

How does pH affect enzyme activity?

Answer 32

Most enzymes can only function within a narrow range of pH. When pH is above or below the optimum pH, the structure of active sities of the enzyme changes which causes the denaturing of the enzyme.

Question 33

How does the substrate concentration affect enzyme activity?

Answer 33

Increase in substrate concentration can increase the chance that a substrate collides with the active site of the enzyme to form the enzyme-substrate complex.

Question 33

How does the enzyme concentration affect enzyme activity?

Answer 33

Increase in enzyme concentration can increase the chance that a substrate collides with the active site of the enzyme to form the enzyme-substrate complex.