Chapter 6- Exchange

Question 1

How do organisms transfer materials between two environments

Answer 1

• transfer occurs at exchange surfaces
• always involves crossing cell plasma membranes

Question 2

What are the two ways exchange can take place

Answer 2

1. passively- no energy required by diffusion and osmosis
2. actively- energy required by active transport

Question 3

Features of specialised exchange surfaces

Answer 3

• large SA
• very thin so that the diffusion distance is short
• selectively permeable to allow selected materials across
• a transport system to ensure the movement of the internal medium to maintain a diffusion gradient

Question 4

What’s the internal network of tubes in an insect for gas exchange called

Answer 4

tracheae which then divide into dead-end tubes called tracheoles

Question 5

In insects what are the three ways gases move in and out of the tracheal system

Answer 5

1. along a diffusion gradient
2. mass transport- contraction of muscles can squeeze trache allowing air to be pushed along
3. ends of tracheoles are filled with water- can carry out anaerobic respiration

Question 6

Describe the spiracles on the tracheae

Answer 6

• tiny pores on the body surface
• the spiracles can be opened and closed by a valve

Question 7

What are some limitations of the tracheal system

Answer 7

• relies mostly on diffusion to exchange gases
• insects have to be small to make sure the diffusion pathway is short

Question 8

Describe the structure of the gills

Answer 8

• made of gill filaments stacked up in a pile
• gill lamellae at right angles to the filaments which increase the SA of the gills
• they face in opposite direction to the water ( countercurrent flow) to increase amount of water flowing over them

Question 9

Describe the countercurrent exchange principle

Answer 9

• oxygenated blood meets water, diffusion of oxygen from the water to the blood takes place
• deoxygenated blood meets water, diffusion of oxygen from water to blood takes place

Question 10

How is gas exchanged in the leaf of a plant

Answer 10

• photosynthesis- plant takes in CO2 and produces O2
• most of the CO2 is obtained from the external air and oxygen produced diffuses out of the plant
• at night oxygen diffuses into the leaf and CO2 diffuses out

Question 11

Describe the structure of a plant leaf and gas exchange

Answer 11

• no living cell is far from the external air meaning there is a short, quick diffusion pathway
• diffusion takes place in the gas phase of diffusion so its more rapid than in water

Question 12

Adaptions a plant has for efficient gas exchange

Answer 12

• many small pores called stomata to make a small diffusion pathway
• many interconnecting air spaces that occur throughout the mesophyll
• large SA of mesophyll cells for rapid diffusion

Question 13

Describe the stomata

Answer 13

• minute pores on the underside of leaves
• each stoma is surrounded by a pair of specialised cells called guard cells which can open and close the stomatal pore
• they are able to close the stoma to reduce water loss as terrestrial organisms lose water by evaporation

Question 14

How do insects limit water loss

Answer 14

evolved adaptions including:
- small SA to Vol ratio
- waterproof coverings
- spiracles

Question 15

How do plants limit water loss

Answer 15

• thick waxy cuticle
• rolling up of leaves
• hairy leaves
• stomata in pits or grooves
• a reduced SA to Vol ratio

Question 16

Why do aerobic organisms need a constant supply of oxygen

Answer 16

in order to release energy in the form of ATP in respiration

Question 17

What are the lungs

Answer 17

• site of gas exchange in mammals
• they are protected by the ribcage
• they are ventilated by a constant supply of air

Question 18

Name some parts of the human gas exchange system

Answer 18

• lungs
• trachea
• bronchi
• bronchioles
• alveoli

Question 19

What is:
1. inspiration
2. expiration

Answer 19

1. when the air passage of the atmosphere is greater than the air pressure inside of the lungs, air is forced into the lungs
2. when the air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs

Question 20

What 3 muscles help with breathing

Answer 20

1. diaphragm- sheet of muscle that separates the thorax from the abdomen
2. internal intercostal muscles- contraction leads to expiration
3. external intercostal muscles- contraction leads to inspiration

Question 21

What is the structure of the human digestive system

Answer 21

its made up of long muscular tubes and its associated glands
-the glands produce enzymes to hydrolyse large molecules into smaller ones ready for absorption

Question 22

Name 3 major parts of the digestive system

Answer 22

• oesophagus
• stomach
  -ileum
• large intestine
• rectum
  -salivary glands
• pancreas

*look on pages 151/152 for explanations

Question 23

What are the two stages of digestion

Answer 23

1. physical breakdown- structures such as teeth break down food into smaller parts to create a larger SA for chemical digestion
2. chemical digestion- hydrolyses large insoluble molecules into smaller, soluble ones

Question 24

What are the three digestive enzymes

Answer 24

1. carbohydrase- hydrolyses carbohydrates to monosaccharides
2. lipases- hydrolyses lipids to glycerol and fatty acids
3. proteases- hydrolyses proteins to AA’s

Question 25

What is emulsification

Answer 25

where lipids are split into tiny droplets called micelles by bile salts

Question 26

What are the three different types of peptidases

Answer 26

1. endopeptidases- hydrolyse the peptide bonds between AA’s in the central region
2. exopeptidases- hydrolyse peptide bonds on the terminal AA’s
3. dipeptidases- hydrolyse the bond between the two amino acids of a dipeptide

Question 27

Structure of the ileum

Answer 27

• wall of ileum has villi which increase the SA therefore increasing rate of absorption

Question 28

Properties of villi which increase efficiency of absorption

Answer 28

• they increase SA for diffusion
• very thin walls to decrease diffusion distance
• contain muscle so can maintain a diffusion gradient
• well supplied with blood vessels which can absorb molecules
• villi have microvilli which increase SA further