Topic 1: Cells, enzymes, diffusion

Question 1

How are egg cells adapted for their purpose?

Answer 1

Function is to Carry the female DNA and nourish the developing embryo in early stages:
- Nutrients in the Cytoplasm to feed the Embryo
- Has a Haploid Nucleus
- Membrane changes structure after fertilisation to prevent any more sperm from getting in, so the offspring have the right amount of DNA

Question 2

How are sperm cells adapted for their purpose?

Answer 2

Function is to transport the male’s DNA to the female’s egg:
- Long tail to swim to the egg
- Lots of mitochondria in the middle section to provide the energy (from respiration) needed to swim to the egg
- Acrosome at front of head where it stores enzymes needed to digest its way through the membrane of the egg cell
- Contains a Haploid Nucleus

Question 3

Explain ciliated epithelial cells

Answer 3

• Line the surface of organs
• Some have cilia (hair-like structures) on the surface of the cell which beat to move substances in one direction, along the surface of the tissue
• e.g. lining of airways contains lots of ciliated epithelial cells to move mucus up to the throat so it is swallowed and doesn’t reach the lungs

Question 4

Explain what happens when an egg is fertilised

Answer 4

Nucleus of an egg fuses with the nucleus of a sperm cell to create a fertilised egg which develops into an embryo
The nucleus of sperm and egg cells contains half the number of chromosomes that’s in a normal body cell and are ‘haploid’ so that when combined, they have the right number of chromosomes

Question 5

What’s the food test for Sugars?

Answer 5

Benedict’s Test
- Add benedict’s reagent to sample and heat in a 75’C water bath
- If solution forms a coloured precipitate, it contains sugars
Stays blue = no sugar
Green (low conc. of sugar) –> Yellow –> Orange –> Brick Red (highest conc.)

Question 6

What’s the food test for Starch?

Answer 6

Iodine
- Add a few drops of iodine to sample
- If starch is present, it will turn from brown-orange to blue-black

Question 7

What’s the food test for Lipids?

Answer 7

Emulsion Test
- Add a few drop of ethanol to sample and shake for 1 minute
- Once dissolved, pour solution into water
- If Lipids are present, they will precipitate out of the liquid and show up as a milky emulsion

Question 8

What’s the food test for Proteins?

Answer 8

Biuret Test
- Add potassium hydroxide solution to sample to make it alkaline
- Add bright blue copper sulphate solution
- If it turns purple, proteins are present

Question 9

What are enzymes?

Answer 9

Biological catalysts that speed up chemical reactions in the body
- They reduce the need for high temperatures

Question 10

Explain the ‘lock and key’ mechanism in terms of enzymes

Answer 10

Every enzyme has an active site which joins onto a substrate to catalyse the reaction.
Enzymes have a high specificity for their substrate as they usually only work with one substrate
this is because, for an enzyme to work, the substrate has to fit into the active site and if it doesn’t match the active site’s shape then the reaction won’t be catalysed.

Question 11

Explain how temperature affects rates of reaction in the body

Answer 11

Changing the temperature changes the rate of enzyme-catalysed reaction
At first, higher temperatures increase the rate
but if it gets too hot, some of the bonds holding the enzyme together break which changes the shape of the active site so the substrate no longer fits and the enzyme is said to be denatured

(THIS IS THE SAME FOR PH, THEIR OPTIMUM PH IS USUALLY 7 APART FROM PEPSIN WHERE IT IS 2)

Question 12

Explain how substrate concentration affects rates of reaction

Answer 12

• Higher the substrate concentration, the faster the reaction as it increases the likelihood that the enzyme will meet up and react with a substrate molecule
• However, after a certain point there are so many substrate molecules that all of the active sites are full, so adding more makes no difference

Question 13

What’s the formula for rate of reaction when given the time taken?

Answer 13

1000/Time

Question 14

How do you calculate the rate of reaction when an experiment measures how much something changes over time?

Answer 14

Change/Time

Question 15

Why do some bigger molecules need to be broken down into smaller components?

Answer 15

So they can be used for growth and other life processes

Question 16

Give 2 examples of the Humans and Plants breaking down big molecules

Answer 16

• Food molecules we eat are too big to pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules which can pass easily through walls in the digestive system allowing them to be absorbed into the bloodstream. They can then pass into cells to be used by the body.
• plants store energy in the form of starch. When the plant needs energy, enzymes break down the starch into smaller molecules (sugars) which can be respired to transfer energy to be used by the cells.

Question 17

Explain the role of enzymes in converting carbohydrates

Answer 17

Enzymes called carbohydrases convert carbohydrates into simple sugars
e.g. Amylase breaks down starch into maltose

Question 18

Explain the role of enzymes in converting proteins

Answer 18

Proteases convert proteins into amino acids

Question 19

Explain the role of enzymes in converting lipids

Answer 19

Lipases convert lipids into glycerol and fatty acids

Question 20

How can we investigate the effect of pH on enzyme activity?

Answer 20

• drop of iodine solution into every well on a spotting tile (control)
• Add 3cmcubed of Amylase solution and 1cmcubed of pH 5 buffer solution to a boiling tube and place in a 35’C water bath and wait 5 minutes
• Add 3cmcubed of starch solution to the boiling tube and immediately mix the contents and start a stop watch
• Every 10 seconds put a drop into a different well of iodine solution and it should turn blue black at first
• When the iodine solution remains orange-brown, starch is no longer present
• Repeat experiment with buffer solutions with different pH values

CONTROL VARIABLES - Concentration and volume of amylase solution
PROBLEMS - Only an approximate time as it is every 10 seconds

Question 21

Which enzyme aids in making glycogen?

Answer 21

Glycogen synthase is an enzyme that joins chains of glucose molecules to make glycogen (molecule used to store energy in animals)

Question 22

How can carbohydrates and proteins be synthesised?

Answer 22

Carbohydrates can be synthesised by joining together simple sugars
Proteins can be synthesised by joining amino acids together
(enzymes catalyse the reactions needed to do this?

Question 23

Define Diffusion

Answer 23

The net movement of particles from an area of higher concentration to an area of lower concentration

Question 24

What state does diffusion occur in and why?

Answer 24

Liquids and gases - the particles are free to move about randomly

Question 25

What types of molecules can diffuse?

Answer 25

• Only small molecules can diffuse through cell membranes e.g. glucose, amino acids, water, oxygen
• Big molecules (e.g. starch, proteins) can’t fit through the membrane

Question 26

Define Osmosis

Answer 26

The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
OR
……from a region of lower solute concentration to a region of higher solute concentration

Question 27

Can water molecules pass through the membrane both ways during osmosis?

Answer 27

YES - the water molecules can pass both ways through the membrane during osmosis because they move about randomly all the time

Question 28

Define Active Transport

Answer 28

The movement of particles across a membrane against a concentration gradient, using energy transferred during respiration

Question 29

What experiment could you do to investigate Osmosis?

Answer 29

1) Prepare sucrose solutions of different concentrations ranging from pure water to very concentrated sucrose solution
2) Use a cork borer to cut a potato into the same sized pieces from the same potato (approx. 1cm diameter)
3) Divide cylinders into groups of 3 and use a mass balance to measure the mass of each group
4) Place one group in each solution
5) Leave them in the solution for at least 40 minutes
6) Remove them and pat them dry, weigh each group again

Question 30

How do you calculate percentage change?

Answer 30

Change/original x 100