73 1 single wastes reproducing small volume diffusion

7.3
1
• single • wastes • reproducing • small • volume • diffusion
• organelles • transport • larger • specialised • organs • alive
2 1:5, 2:4, 3:1, 4:6, 5:2, 6:3
3
a) It acts as a protective barrier for our bodies.
b) Skin cells are programmed to die when they reach the outer most layer of
skin. Here the dead cells form a thin, scaly mesh that is water-proof and
acts as a barrier to microbes from entering the body.
4
a) Around 3.8 billion years ago ( bya )
b) More than 30 times
c) It allows increased organism size; internal parts have protection from
outer cells – including reproductive cells; parts of the organism can die
while the rest of the organism survives.
d) To fulfil specific functions that suit their position relative to the other cells
e.g. outside cells tend to have a role as a protective barrier.

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22
Chapter 8
Section Activity Sample answers
8.1 1
Across:
1. Light
4. Leaf
6. ATP
10. Respiration
12. Glucose
13. Chlorophyll
14. Water
15. Anaerobic
17. Starch
18. Oxygen
19. Carbon dioxide
20. Carbon dioxide
Down:
2. Heterotroph
3. Water
5. Autotroph
7. Plant
8. Chloroplast
9. Mitochondria
11. Photosynthesis
16. Oxygen
8.3
1
• Salts – Inorganic – Na + – Help nerves to function
• Carbohydrates – Organic – Sugars, pastas – Used for energy
• Lipids – Organic – Fats, oils – Energy storage, cell membranes, insulation
• Proteins – Organic – Meats, eggs – Growth and repair
• Vitamins – Organic – B group – Help enzymes function, regulate cell
activities, assist metabolism and growth
2
Sugar is very important for having energy as an organism. However, many
other substances are derived from foods that are not sugars and are essential
for the healthy functioning of an organism. For example, fats in food are
useful for energy storage and vitamins are needed to allow enzymes to
function correctly.
8.4 1
a) Our digestive system from the mouth to the anus is like a donut hole, as
food passing through it is not part of the body, just as something in a
donut hole is not inside the donut itself.
b) Water, mucous, and the enzyme amylase.
c) Help churn the food.
d) Hydrochloric acid creates an acid environment to allow pepsin to start
breaking down proteins.
e) Bile salts surround lipids to assist in breaking them down.
f) They help break down different substances in food.
g) Nutrients move by diffusion and active transport into the cells and
capillaries of the intestinal lining.
h) Water is absorbed from waste and bacteria here help to release vitamins
from the food.
i) In herbivores, the appendix helps to break down cellulose. However, in
humans, who eat much less cellulose in their diet, the appendix is not
involved in digesting cellulose.

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23
Chapter 8 [continued]
Section Activity Sample answers
8.4
2
Clockwise from bottom left:
• appendix • large intestine • gall bladder • liver
• stomach • pancreas • small intestine • rectum
3
Mouth :
• Chemical: releases saliva containing enzymes, e.g. amylase
• Physical: teeth cut/grind food, which increases its surface area
Stomach :
• Chemical: releases acid and enzymes such as pepsin
• Physical: muscles churn food
Small intestine:
• Chemical: contains many different enzymes to break down food
8.5
1
a) Faeces
b) It is eliminated as faeces.