2.7-5.6 Cellular processes

Question 1

What are carbohydrates composed of?

Answer 1

Made up of simple sugars
Carbon, hydrogen and oxygen
Large complex carbohydrates are made up of many smaller units joined together in a long chain e.g. starch and glycogen made up of glucose or maltose

Question 2

What are proteins composed of?

Answer 2

Carbon, nitrogen, hydrogen and oxygen

Made up of amino acids

Question 3

What are lipids made up from?

Answer 3

Fatty acids and glycerol

Contain carbon, hydrogen and oxygen

Question 4

Describe the test for glucose

Answer 4

Benedict’s test
- Place 5cm^3 of a food sample to a test tube
- Set a water bath to 75C
- Add some Benedict’s solution to the test tube using a pipettes
- Place the test tube in the water bath (test tube holder) and leave it in there for 5 minutes.
Glucose present: blue —> green/yellow (low conc) or brick red (high conc)

Question 5

Describe the test for starch

Answer 5

Iodine Solution
- Add 5cm3 of food sample to a test tube
-Add a few drops of iodine solution and gently shake
Brown-orange –> blue-black

Question 6

Describe the test for protein

Answer 6

Biuret test
- Add 2cm3 of the food sample to a test tube
- Add 2cm3 of buret solution and gently shake
Blue–>pink or purple

Question 7

Describe the test for lipids

Answer 7

Sudan III test
- Add 5cm3 of the food sample to a test tube
-Add 3 drops of Sudan III stain solution and gently shake
Will separate into two layers –> top layer = bright red

Question 8

Define an enzyme

Answer 8

• Biological catalyst (increases the speed of a reaction without being changed or used up)
• Reduce the need for high temperatures for increasing rate of reactions
• Used to speed up metabolic reactions (useful reactions)
• Is a protein = made up of chains of amino acids

Question 9

Describe the ‘lock and key’ model

Answer 9

Substrate joins onto the active site of an enzyme which is complementary to form an enzyme substrate complex

Question 10

How does temperature change affect enzyme function?

Answer 10

Increase in temperature = Increases the rate of reaction
Enzymes and substrates have more energy - more likely to form enzyme-substrate complexes
HOWEVER past the optimum temperature the enzyme denatures and enzyme active site change shape

Question 11

How does pH change affect enzyme activity?

Answer 11

Too high or too low, denature and active site changes shape

Question 12

Describe an experiment to investigate the effect of temperature on enzyme activity (how fast a product appears)

Answer 12

-Use a pipette add 10cm3 of hydrogen peroxide to a boiling tube in a water bath at 10C
-Add a source of catalase (1cm3 of potato) and put a delivery tube from the test tube to an upside down measuring cylinder full of water
-Record how much oxygen is produced in 1 minute
-Repeat 3 times and mean
-Repeat at 20C, 30C and 40C
Control variables = pH, species of potato, size of potato

Question 13

Describe an experiment to investigate the affect of temperature on enzyme activity (how fast a substrate disappears)

Answer 13

• Put a mixture of starch solution and amylase enzyme in a test tube then into a water bath at 20C
• Put a drop of iodine solution into each well on a spotting tile
• Every ten seconds, drop a sample of the mixture into a well using a pipette
• When the iodine solution remains browny-orange record the total time taken (starch not present)
• Repeat with water bath at different temperatures

Question 14

Describe an experiment to investigate how pH affects enzyme activity

Answer 14

Adapt the temperature experiments –> follow the same method, but add a buffer solution with a different pH level to a series of different tubes containing the enzyme-substrate mixture
Keep volumes, concentrations and temperature same (use water bath)

Question 15

Define diffusion

Answer 15

The random, net movement of particles from an area of high concentration to an area of low concentration

• Doesn’t require energy
• In liquids and gases

Question 16

How do substances diffuse in and out of cells

Answer 16

Cell membranes let substances in and out
Only very small molecules can diffuse through cell membranes e.g. glucose, amino acids, water and oxygen (starch, proteins can’t)
From higher conc to low conc (random so go both ways but net movement from higher conc side)

Question 17

Define osmosis

Answer 17

The net movement of water molecules from an area of high water potential to an area of low water potential across a semi permeable membrane

Question 18

What is hypertonic

Answer 18

Concentration higher outside the cell than inside (lower water potential outside the cell) - water moves out of the cell

Question 19

What is isotonic

Answer 19

Same concentration inside and outside (equal movement)

Question 20

What is hypotonic

Answer 20

Less concentrated outside than inside (high water potential outside cell) - water moves into the cell

Question 21

What happens if a plant cell is placed in pure water?

Answer 21

• High water potential outside the cell (water moves into the cell)
• Cell will swell up, the cytoplasm pushes against the cell wall –> developed an internal pressure = TURGID

Question 22

What happens if a plant has turgid cells?

Answer 22

It will get more light on the leaves for photosynthesis

Question 23

How do plant cells become plasmolysed?

Answer 23

• Cell is placed in a hypertonic solution = higher water potential INSIDE the cell
• Water will move out of the cell into the solution via osmosis
• Cell will decrease in volume, cytoplasm does not push against the cell wall (Flaccid)
• If this continues, the membrane pulls away from the cell wall (Plasmolysed)

Question 24

What would happen if you placed an animal cell in a pure water solution?

Answer 24

• Swell up and burst

- Do not have a cell wall so cannot resist the internal pressure caused by water moving into them

Question 25

What would happen if you placed an animal cell in a concentrated solution?

Answer 25

Shrink and produce cells with crinkly edges

Question 26

Describe osmosis in the body

Answer 26

• Tissue fluid (water with oxygen, glucose etc) surrounds the cells in the body
• Squeezed out of the blood capillaries to supply the cells
• Different concentration to the fluid inside the cell so the water will move from the tissue fluid to the cell or out of the cell via osmosis

Question 27

Describe an experiment to investigate diffusion in a non-living system

Answer 27

1. Make up some agar jelly with phenolphthalein and dilute sodium hydroxide - pink in colour
2. Cut of a few cubes of the jelly and put them in a beaker of dilute hydrochloric acid
3. Turn colourless as the acid diffuses into the agar jelly and neutralised the sodium hydroxide

Question 28

How would you adapt this diffusion experiment to find the rate of diffusion?

Answer 28

Use different sized cubes of agar jelly and timing how long it takes for the cube to go colourless
The cube with the largest surface area to volume ratio will lose its colour quickest

Question 29

Describe an experiment to investigate osmosis in a living system

Answer 29

1. Label 6 boiling tubes with the concentration of 2o cm3 sucrose solutions detailed in the table from 0-1.0 with 0.2M intervals (0M use distilled water)
2. Cut 6 potato cylinders - 5cm long - using the borer, scape and white tile
3. Measure the length of the cylinders then leave them in a test tube each for 30 mins then take them out and measure again
4. Taken in water by osmosis = longer , Water given out = shrunk

Question 30

Describe an experiment to investigate osmosis in non-living systems - risking tubing

Answer 30

1. Fix some Viking tubing over the end of a thistle funnel. Then pour some sugar solution down the glass tube into the thistle funnel
2. Put the thistle funnel into a beaker of pure water - measure where the sugar solution comes up to on the glass tube
3. Leave overnight, then measure where the solution is in the glass tube. Water should be drawn through the Visking tubing by osmosis and this will force the solution up the glass tube

Question 31

Define active transport

Answer 31

The random movement of particles against a concentration gradient (area of low concentration to an area of high concentration) using energy (released during respiration)

Question 32

Give an example of when active transport is used in the body

Answer 32

1) When there is a lower concentration of nutrients in the gut than in the blood this means the concentration gradient is the wrong way and the nutrient would go from blood–> gut
2) Active transport allows nutrients to be taken into the blood despite the concentration gradient being the other way using energy from respiration to stop us starving

Question 33

Give an example of when active transport is used in plants

Answer 33

How they get minerals from the soil to root hair cells (low–> high)

Question 34

What are the four factors that affect the movement of substances?

Answer 34

1) Surface area to volume ratio e.g. smaller cube has a larger surface area to volume ratio and means substances would move faster
2) Distance - short distance = faster
3) Temperature - warmer means more energy = faster movement
4) Concentration gradient - move faster if there is a steeper conc gradient *Conc gradients do not affect active transport