Required Practical 8

Question 1

the seed coat of each bean was removed and discarded.

suggest why?

Answer 1

better release of mitochondria

Question 2

what is meant by isotonic?

Answer 2

same water potential as variable e.g. in this case MITOCHONDRIA

Question 3

why were the beans blended?

Answer 3

release mitochondria from cells

Question 4

the cloth was moistened with isolation medium and not moistened with water.

explain why water was not used to moisten the cloth?

Answer 4

• water would affect WP
• as has higher WP
• water would enter mitochondria by OSMOSIS

Question 5

the mixture was poured through cloth to filter it.

give 2 reasons why it was necessary to filter the mixture?

Answer 5

• to remove cell debris
• remove large organelles

Question 6

why was the mitochondrial suspension kept on ice before use?

Answer 6

reduce enzyme activity

Question 7

succinate was added to the suspension of mitochondria as a respiratory substrate.

explain why glucose could NOT be used as the respiratory substrate in this investigation?

Answer 7

• glucose too big to cross mitochondrial membrane
• no cytoplasm
• so no glycolysis

Question 8

in tube A were the following:

• 5 cm3 succinate sol
• 2cm3 mitochondrial suspension
• 10 drops DCPIP

the contents of tube A did not go colourless.

suggest one reason why?

Answer 8

mitochondrial suspension still present

Question 9

addition of succinate to mitochondria leads to electron transfer.

what leads to electron transfer in chloroplast investigation?

explain your answer?

Answer 9

• light
• light excites chlorophyll

Question 10

how much chloroplast suspension, DCPIP, distilled water and isolation medium would you put in a control tube?

Answer 10

• 0 cm3 chloroplast suspension
• 5cm3 DCPIP
• 1cm3 distilled water
• 1cm3 isolation medium

Question 11

you were told not to put the leaf midrib or leaf stalk in blender.

why?

Answer 11

contain less chloroplasts

Question 12

what is the purpose of using a blender?

Answer 12

break open organelles

Question 13

the isolation medium was cold and was also isotonic with the spinach tissue.

explain why it was important that the isolation medium was cold?

Answer 13

• reduce enzyme activity
• enzymes released during blending
• chloroplast not damaged

Question 14

explain why it was important that the isolation medium was isotonic with the spinach tissue?

Answer 14

• so WP same as plant tissue
• chloroplasts dont burst

Question 15

there are large pieces of tissue and other organelles in your chloroplast suspension.

describe how you could isolate the chloroplasts from the other components in the suspension?

Answer 15

• filter using centrifuge
• at low speed then high speed
• collect pellets

Question 16

you were told to wrap up a tube in aluminium foil.

why?

Answer 16

prevent entry of light

Question 17

tube B was a control experiment.

explain how the results of this tube acted as a control?

Answer 17

• no colour change
• colour change not due to isotonic medium
• is due to chloroplasts

Question 18

name the part of chloroplast where electron transfer takes place?

Answer 18

thylakoid membrane

Question 19

DCPIP is decolourised more slowly when ammonium hydroxide is added.

use your knowldege of LDR to suggest why?

Answer 19

• ammonium hydrox slows electron transfer
• along ETC

Question 20

some weed killers are substances that accept electrons during photosynthesis.

suggest how these substances kill weeds?

Answer 20

• slow LDR
• less production of NADPH

Question 21

suggest disadvantages of using weed killers on weeds growing in crop.

explain answer?

Answer 21

• susbstance in weed killer absorbed by crop - reduces yield of crop
• toxic effects of crop on wildlife when eaten
• slows respiration