Topic 3: Organisms exchange substances with their environments

Question 1

What is the relationship between size of an organism and it’s surface area to volume ratio?

Answer 1

The larger the organism, the smaller it’s surface area to volume ratio.

Question 2

How does gas exchange occur in single celled organisms?

Answer 2

Substances can diffuse directly into and out of the cell across the cell surface membrane, the diffusion rate is quick due the short distance the substances have to travel.

Question 3

Why can diffusion across the outer membrane not occur in multicellular organisms?

Answer 3

1. Some cells are too deep within the body so there is a longer diffusion distance#
2. larger animals have a smaller surface area to volume ratio - hard to exchange enough substances to supply a large volume of animal through a relatively small outer surface.

Question 4

What is the relationship between surface area to volume ration and heat loss?

Answer 4

The smaller an organisms surface area to volume ratio the harder it is for them to lose heat.

Question 5

What do smaller organisms that are vulnerable to heat loss need to generate enough heat to stay warm?

Answer 5

A high metabolic rate.

Question 6

What is the relationship between body shape and heat loss?

Answer 6

Animals with a compact shape have a small surface area to volume ratio minimising heat loss. Animals with a less compact shape have a larger surface area to volume ratio, this increases heat loss.

Question 7

What are some other adaptations that animals have to aid exchange?

Answer 7

1. To support their high metabolic rates small mammals in cold regions need to eat large amounts of high energy foods like seeds and nuts.
2. Smaller mammals may have thick layers of fur or hibernate when the weather gets really cold.
3. Larger organisms in hot regions find it hard to keep cool so animals like elephants have developed large flat ears to increase their surface areas allowing them to lose more heat. Hippos spend much of the day in water.

Question 8

What adaptations of a gas exchange surface increase the rate of gas exchange?

Answer 8

1. Large surface area
2. Very thin to provide a short diffusion pathway
3. Steep concentration gradient.

Question 9

What are the gill filaments?

Answer 9

Each gill is made up of thin plates called gill filaments which increase the surface area.

Question 10

What are the gill lamellae?

Answer 10

Positioned at right angels to the gill filaments and further increase the surface area. Also have lots of blood capillaries whcih are very close to the outside and a thin surface layer of cells.

Question 11

What is the counter current principle?

Answer 11

Blood flows through the lamellae in one direction and water flows over them in the opposite direction.

Question 12

What does the counter current system ensure?

Answer 12

That equilibrium is never reached so diffusion can occur across the entire length of the gill lamellae.

Question 13

Where is the main gas exchange surface in plants?

Answer 13

The mesophyll cells in the leaf.

Question 14

How do leaves prevent water loss?

Answer 14

Guard cells close the stomata at night when photosynthesis doesn’t occur.

Question 15

How does water entering and leaving control the stomata?

Answer 15

• Water enters the guard cells making them turgid which opens the stomata.
• Water leaves the guard cells making them flaccid which closes the stomata.

Question 16

What are xerophytic plants?

Answer 16

Plants that are adapted to survive in warm,dry or windy habitats where water loss is a problem.

Question 17

What are some examples of xerophytic adaptations which help to minismise water loss?

Answer 17

1. Curled leaves with the stomata inside, protecting them from the wind. Also traps water vapour and increases local humidity which reduces the water potential gradient between the air and the leaf so reduces evaporation.
2. Hairs on the epidemis trap water vapour around the stomata.
3. Stomata sunk in pits to trap water vapour.
4. A reduced number of stomata so there are fewer places for water to escape.
5. Thicker waxy, waterproof cuticles on leaves and stems to reduce evaporation.
6. Longer root network to reach more water.

Question 18

What adaptations to leaves have to increase the rate of diffusion?

Answer 18

1. A flat broad shape to increase surface area.
2. Very thin and flat to decrease diffusion pathway.
3. Lots of stomata
4. Air spaces to maintain a concentration gradient.

Question 19

What are the components of the tracheal system?

Answer 19

1. The spiracles
2. The trachea
3. The tracheoles

Question 20

What are the spiracles?

Answer 20

Small holes on the abdomen that allow gases to diffuse in and out.

Question 21

What is the trachea?

Answer 21

Microscopic air filled pipes that attach to the spiracles, it is a network of internal tubes with rings to strengthen them and keep them open.

Question 22

What are the tracheoles?

Answer 22

Trachea branch into tracheoles deeper into the abdomen. They have thin permeable walls and go to individual cells to deliver oxygen and remove carbon dioxide.

Question 23

What are the methods of moving gases into the tracheal system?

Answer 23

1. Gas exchange by diffusion.
2. Mass transport- insects use rythmic abdominal movements to moves gases in and out.

Question 24

How is the tracheal system adapted for efficient gas exchange?

Answer 24

1. many highly branched tracheoles increase the surface area.
2. Tracheoles have thin walls so short diffuion distance.
3. Steeo concentration gradient maintained as cells constantly using up o2 for respiration.

Question 25

How do insects minimize their water loss?

Answer 25

1. Muscular sphincters control the opening and closing of the spiracles. 2. Have a waterproof waxy cuticle and hairs around the spiracles to reduce evaporation. 3. Have a waterproof exoskeleton made of chitin.

Question 26

What are the components of the human gas exchange system?

Answer 26

1. Trachee 2. Bronchi 3. Bronchioles 4. Alveoli

Question 27

What happens during inspiration?

Answer 27

The external intercostal muscles and diaphragm contract and the internal intercostal muscles relax. The ribcage moves upwards and outwards and the diaphragm flattens increasing the volume of the thorcaic cavity. This causes the air pressure to decrease below atmospheric pressure Air flows down the trachea into the lungs down the pressure gradient. Inspiration is an active process.

Question 28

What happens during expiration?

Answer 28

External intercostal muscles and diaphragm relax and the internal intercostal muslces contract. The ribcage moves downwards and inwards and the diaphragm curves upwards returning to it's dome shape. The volume of the thorcaic cavity decreases causing the pressure to increase above atmospheric pressure. Air is forced down the pressure gradient and out of the lungs. Normal expiration is a passive process.

Question 29

What word is used to describe the interaction between the internal and external intercostal muscles?

Answer 29

Antagonistic.

Question 30

What is the alveolar epithelium?

Answer 30

A single layer of thin flat cells that make up the walls of each alveolus.

Question 31

What are the walls of capillaries made of?

Answer 31

Capillary endothelium.

Question 32

What does the protein Elastin do?

Answer 32

Helps the alveoli return to it's normal shape after inhaling and exhaling air.

Question 33

How does oxygen move from the atmosphere into the blood?

Answer 33

Moves down the pressure gradient from the atmosphere into the alveoli. It diffuses out of the alveoli across the alveolar epithelium and the capillary endothelium and inot haemoglobin. CO2 moves in the opposite direction.

Question 34

What are the adaptations of the alveoli that speed up the rate of gas exchange?

Answer 34

1. Thin exchange surface - the alveolar epithelium is only 1 cell thick. So there is a short diffusion pathway. 2. A large surface area - there are millions of alveoli. 3. Steep concentration gradient of O2 aand CO2 between the alveoli and capillaries. maintained by flow of blood and ventilation.

Question 35

What is tidal volume?

Answer 35

The volume of air in each breath - usually between 0.4dm3 and 0.5dm3 for adults.

Question 36

What is ventilation rate?

Answer 36

The number of breaths per minute. For a healthy person at rest it's about 15 breaths.

Question 37

What is forced expiratory volume1?

Answer 37

The maximum volume of air that can be breathed out in 1 second.

Question 38

What is forced vital capacity?

Answer 38

The maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in.

Question 39

How does tuberculosis affect lung function?

Answer 39

Caused by bacteria. The immune system cells build a wall around the bacteria in the lungs forming small hard lumps called tubercles. Infected tissue within the tubercles dies and the gaseous exchange surface is damaged so tidal volume is decreased meaning less air can be inhaled with each breath. Have a faster ventilation rate. Symptoms include a persistent cough, coughing up blood and mucus, chest pains, shortness of breath and fatigue.

Question 40

How does fibrosis affect lung function?

Answer 40

Formation of scar tissue in the lungs caused by an infection or exposure to asbestos or dust. Scar tissue is thicker and less elastic than normal lung tissue. Lungs are less able to expand so tidal volume and FVC is reduced. Reduced rate of gas exchange due to thicker membrane. have a faster ventilation rate. Symptoms include shortness of breath, a dry cough, chest pain and weakness.

Question 41

How does asthma affect lung function?

Answer 41

Airways become inflamed and irritated normally becuase of an allergic reaction. During an asthma attack the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced. This causes constriction of the airways making it hard to breathe properly . Air flow in and out of the lungs is severely reduced so less o2 enters the alveoli and moves into the blood. FEV1 is severely reduced. Symptoms include wheezing, a tight chest and shortness of breath. Symptoms can be relieved by drugs.

Question 42

How does emphysema affect lung function?

Answer 42

Disease caused by smoking or long term exposure to air pollution. Particles get trapped in the alveoli causing inflammation which attracts phagocytes to the area. The phagocytes produce an enzyme that break down elastin. This means that the alveoli can't recoil to expel air as well, also leads to the destruction of the alveoli walls reducing the surface area so rate of gas exchange reduces. Symptoms include shortness of breath and wheezing . Have an increased ventilation rate.

Question 43

What is the effect of lung disease on gas exchange?

Answer 43

Lung disease effect the rate of gas exchange in the alveoli. less O2 is able to diffuse into the blood so the body cells receive less O2 and rate of aeorbic respiration is reduced. So less energy is released so sufferers often feel tired and weak.

Question 44

What is digestion?

Answer 44

large biological molecules are hydrolysed into small soluable molecules which can be transported across cell membranes.

Question 45

What are carbohydrates hydrolysed into?

Answer 45

Disaccharides and then monosaccharides.

Question 46

What are lipids hydrolysed into?

Answer 46

fatty acids and monoglycerides

Question 47

What are proteins hydrolysed into?

Answer 47

Amino acids

Question 48

Where is amylase produced and where does it act?

Answer 48

Produced in the salivary glands and the pancreas. Released into the mouth and small intestine.

Question 49

How does amylase digest starch?

Answer 49

Hydrolyses the glycosidic bonds in starch to produce maltose.

Question 50

How is maltose broken down?

Answer 50

The enzyme maltase hydrolyses the glycosidic bond in maltose into 2 alpha glucose molecules.

Question 51

What are membrane bound diaccharidases?

Answer 51

Enzymes that are attached to the cell membranes of the epithelial cells lining the ileum. The help break down disaccharides into monosaccharides.

Question 52

How is sucrose broken down?

Answer 52

By the enzyme sucrase into glucose and fructose. Involves hydrolysis of glycosidic bonds.

Question 53

How is lactose broken down?

Answer 53

By the enzyme lactase into glucose and galactose. Involves hydrolysis of glycosidic bonds.

Question 54

How are lipids digested?

Answer 54

By the enzyme lipase which hydrolyses the ester bonds and forms fatty acids and a monoglyceride.

Question 55

Where is lipase produced and where does it act?

Answer 55

Made in the pancreas and released into the small intestine.

Question 56

Where are bile salts produced and stored?

Answer 56

Produced by the liver and stored in the gall bladder.

Question 57

What is the role of bile salts?

Answer 57

Emulsify large lipid droplets into smaller ones to increase the surface for liapse to work on. Bile salts join with monoglycerides to form micelles, this makes the monoglyceride more soluable in water so can be transported tthrough cell membranes.

Question 58

What do endopeptidases do?

Answer 58

hydrolyse peptide bonds within a protein chain.

Question 59

Where are endopeptidases produced and where do they act?

Answer 59

Produced in the stomach and pancreas and released into the stomach and small intestine.

Question 60

What is an example of an endopeptidase and what does it do?

Answer 60

pepsin. released into the stomach by cells in the stomach lining. Only works in acidic conditions.

Question 61

What do exopeptidases do?

Answer 61

Hydrolyse peptide bonds at the ends of protein chains. remove single amino acids from proteins.

Question 62

Where are exopeptidases produced and where do they act?

Answer 62

Produced in the pancreas and released into the small intestine.

Question 63

What are dipeptidases?

Answer 63

exopeptidases that work specifically on dipeptides. They hydrolyse the peptide bond between 2 amino acids.

Question 64

Where are dipeptidases located?

Answer 64

Cell surface membrane of the epithelial cells in the small intestine.

Question 65

How are monosaccharides absorbed into the bloodstream?

Answer 65

- Glucose and galactose are absorbed by active transport with sodium ions via a cotransporter protein. - Fructose is absorbed via facilitated diffusion through a different transporter protein.