Topic 6 - Exchange

Question 1

What are the two main ways insects reduce water loss?

Answer 1

• Their exchange system has a large surface area:volume ratio / small surface area.
  The internal SA is large but the external (where they lose water) is small.
• (Waxy) cuticle over their rigid exoskeleton.

Question 2

How are the spiracles adapted to help maintain the humidity around the opening?

Answer 2

They are able to open and close where water can evaporate / not evaporate. Have hairs around the opening.

Question 3

How does the presence of spiracle hairs help to reduce the rate of water loss from the insect?

Answer 3

Hairs reduce rate of air movement and humid air gets trapped around spiracles. The concentration gradient decreases.

Question 4

How does abdominal pumping move gases into the tracheal system of a locust?

Answer 4

It pushes air in the tracheae out to allow fresher, oxygen rich air to enter the locust when it pushes back in.

Question 5

What is a function of the rings of chitin that support the larger trachea of an insect?

Answer 5

It stops the larger trachea from collapsing / closing up.

Question 6

What is the problem of water for respiration?

Answer 6

Oxygen is not very concentrated in water. Warm water has less dissolved oxygen than cold.

Question 7

What is the structure of fish gills?

Answer 7

• Water taken in through mouth and passed over the gills and out of the operculum.
• Gills comprise of filaments stacked up in a pile, which increases surface area for gas exchange.
• Sprouting upwards from the filaments are the lamellae, they increase the SA.
• Flat plates with very thin surfaces.
• Thin epithelium and good blood supply help maintain a concentration gradient.

Question 8

Why is the countercurrent flow (what fish have) more efficient than if they had parallel flow?

Answer 8

Parallel flow = diffusion gradient only at first part of filament. Equilibrium is met at 50%.
Countercurrent flow = concentration of oxygen in water is always slightly more than the concentration in the blood - diffusion gradient is maintained across the entire width of the gill lamellae. Around 80% of oxygen from the water can be absorbed into blood.

Question 9

Why do fish die when they are taken from the water?

Answer 9

Gills are designed for water. Gill surface are covered in water and they stick together when taken out of the water, which decreases the surface area. Gills can also dehydrate.

Question 10

What are some adaptations xerophytes have evolved to live in areas where water is in short supply?

Answer 10

• Extra thick waxy cuticle (more impermeable).
• Less overall surface area than normal plant leaves = less evaporation.
• Low stomatal density = fewer stomata = less water escapes.
• Sunken stomata (in epidermis) that shelters them from conditions that increase transpiration.
• Stomatal hairs = trap water vapour as it leaves the stomata and creates humid air around stomata. Decreases water potential gradient = decreased rate of transpiration.

Question 11

What is the trachea? Function?

Answer 11

• A flexible airway supported by C shaped rings of cartilage.
• Can collapse slightly to allow food to pass down to oesophagus.
• Walls are made from muscle with ciliated epithelial cells and goblet cells. Goblet cells produce mucus.

Question 12

What are the bronchi? Function?

Answer 12

• Two divisions of the trachea, each leading to one lung.
• Have goblet and epithelial cells and cartilage, but the amount is reduced as the bronchi get smaller.

Question 13

What are the bronchioles? Function?

Answer 13

• A series of branching subdivisions of the bronchi.
• Walls made from smooth muscle lined with epithelial cells. Smooth muscle allows them to constrict so they can control air flow at alveoli.

Question 14

What are the alveoli? Function?

Answer 14

• Minute air-sacs located at the end of the bronchioles.
• Contain collagen and elastic fibres and are made from a single layer of flattened epithelial cells.
• Elastic fibres allow them to stretch as they fill with air when breathing in and then recoil when breathing out.

Question 15

What direction do gases move?

Answer 15

From an area of high pressure to an area of low pressure.

Question 16

How does inspiration work (breathing in)?

Answer 16

1) External intercostal muscles actively contract.
2) Internal intercostal muscles relax.
3) Ribs and sternum move upwards and outwards.
4) Diaphragm contracts and flattens.
5) Volume of thorax increases.
6) Elastic tissue of lungs stretch.
7) Lungs expand.
8) Pressure inside lungs reduced.
9) Air forced into alveoli from atmosphere.

Question 17

How does expiration (breathing out) work?

Answer 17

1) Internal intercostal muscles actively contract.
2) External intercostal muscles relax.
3) Ribs and sternum move down and inwards.
4) Diaphragm relaxes.
5) Volume of thorax reduced.
6) Elastic tissue of lungs recoil.
7) Lung size reduced.
8) Pressure inside lungs increased.
9) Air forced out alveoli into atmosphere.

Question 18

What is pulmonary ventilation?

Answer 18

Volume of air moved into lungs in one minute.

Question 19

What is ventilation rate?

Answer 19

Number of breaths that occur in a minute.

Question 20

What is tidal volume?

Answer 20

Volume of air taken in at each breath when at rest.

Question 21

What is the formula for pulmonary ventilation?

Answer 21

Pulmonary ventilation (dm^3 min^-1) = Tidal volume (dm^3) x Breathing rate (min^-1)

Question 22

The reduced elasticity of the lungs causes breathing difficulty. Explain how.

Answer 22

Less recoil which means less air can be expelled. Causes difficulties with diffusion.

Question 23

During an asthma attack, less oxygen diffuses into the blood from the alveoli. Why?

Answer 23

Airway decreases in size due to thick mucus covering it, and the muscle has contracted, meaning there is a smaller pathway for oxygen (less air breathed in = less oxygen diffused into blood from alveoli).

Question 24

Why is a person with emphysema unable to do vigorous exercise?

Answer 24

The length of diffusion pathway is increased, meaning diffusion of oxygen will be slower. Vigorous exercise will increase breathing rate and aerobic respiration. People with it have less alveoli so less diffusion into blood.

Question 25

What is the human digestive system made up of? What does it do?

Answer 25

Made up of a long muscular tube and its associated glands. Glands produce enzymes that hydrolyse macromolecules into simple molecules for absorption.

Question 26

What are salivary glands?

Answer 26

Secretions contain amylase which catalyses the hydrolysis of starch into maltase.W

Question 27

What is the oesophagus?

Answer 27

Carries food from mouth to stomach. Made up of a thick muscular wall.

Question 28

What is the stomach?

Answer 28

Store and digest food. Has glands which produce enzyme that digest protein. Other glands produce mucus to prevent self digestion.

Question 29

What is the pancreas?

Answer 29

Secretion contains proteases to digest proteins, lipase to digest lipids, and amylase for starch.

Question 30

What is the small intestine?

Answer 30

Food further hydrolysed by enzymes produced in walls and by glands. Inner walls folded into villi and microvilli to increase surface area. Absorbing products of digestion into bloodstream

Question 31

What is the large intestine?

Answer 31

Reabsorbs water into body. Food becomes drier and thicker and forms faeces.

Question 32

What is the rectum?

Answer 32

Faeces stored here before being removed via the anus in a process called egestion.

Question 33

What is physical breakdown and chemical digestion of food?

Answer 33

Physical - Large food broken down into smaller pieces ready for chemical digestion. Chemical - Breaks down large, insoluble molecules into smaller, soluble ones via enzymes.

Question 34

How are carbohydrates digested?

Answer 34

1) Saliva enters mouth from salivary glands, mixed with food during chewing. 2) Catalyses hydrolysis of glycosidic bonds in starch, produces disaccharide maltose. 3) Food swallowed, amylase in saliva denatures in stomach acid, preventing further digestion of starch. 4) Food passed into ileum, mixed with pancreatic juice (contains pancreatic amylase). 5) Catalyses hydrolysis of starch to maltose. 6) Smooth muscle in ileum pushes food along, epithelial lining produces maltase. 7) Maltase catalyses hydrolysis of maltose into glucose disaccharide. 8) Molecule can then be absorbed into epithelial cells.