Chapter 6 Organisms exchange substances with their environment

Question 1

What might affect the exchange rate of an organism

Answer 1

the size of an organism
its metabolic rate

Question 2

Which has a higher SA:Vol, small organisms or large organisms

Answer 2

smaller organisms

Question 3

What is Ficks law

Answer 3

Diffusion ∝ (surface area * difference in concentration) / diffusion distance

Question 4

Describe gas exchange in single-celled organisms

Answer 4

single-celled organisms are small and therefore have a large SA:Vol
oxygen is absorbed by diffusion across their body surface, which is only covered by a CSM
in the same way, CO2 from respiration diffuses out across their body surface

Question 5

What is the problem for gas exchange in insects

Answer 5

cells need to be exposed to air in order for the oxygen to diffuse into the organism
terrestrial organism’s bodies are made of a high % of water
when living cells are exposed to the air = water molecules evaporate and the cell dehydrates

Question 6

how do gasses travel from the environment to the insects cells

Answer 6

Spiracles –> trachea –> tracheoles –> muscle fibres

respiratory gasses move in and out of the tracheal system in three ways:

Along a diffusion greadient
Mass transport
the ends of the tracheoles are filled with water so can move into the cells via osmosis

Question 7

describe the structure of the gills

Answer 7

located behind the head
made up of gill filaments which are stacked up in a pile (like pages in a book)
at right angles to gill filaments are gill lamellae –> increases SA of gill
water is taken in by the mouth and forced over the gills
the flow of water over the gill lamellae and the flow of blood within them are in opposite directions (known as counter current flow)

Question 8

describe the arrangement of gill lamellae for counter current

Answer 8

blood that is already well loaded with oxygen meets water, which has its maximum concentration of oxygen
therefore diffusion of oxygen from the water to the blood takes place
blood with little oxygen in it meets water which has had most, but not all, of its oxygen removed. Again, diffusion of oxygen from the water to blood takes place

Question 9

describe the result of counter current flow

Answer 9

a diffusion gradient for oxygen uptake is maintained across the entire width of the gill lamellae
in this way, 80% of the oxygen available in the water is absorbed into the blood of the fish (rather than 50% if it was parallel flow)

Question 10

What is the difference between animals and plants when it comes to gas exchange

Answer 10

plants need to photosynthesise (which incudes CO2 and oxygen)

Question 11

Describe the balance of gases during photosynthesis

Answer 11

When photosynthesis is taking place
- although some CO2 comes from respiration of cells, most of it is obtained from the external air
- In the same way, some oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant

Question 12

Describe the balance of gases when photosynthesis isn’t occurring

Answer 12

• oxygen diffuses into the leaf because it is constantly being used by cells during respiration
• In the same way, CO2 produced during respiration diffuses out

Question 13

In what ways is gas exchange in plants similar to that of insects

Answer 13

no living cell is far from the external air, and therefore a source of oxygen and carbon dioxide
Diffusion takes place in the gas phase (air), which makes it more rapid than if it were in water

Question 14

Describe how a plant is structured for efficient gas exchange

Answer 14

short, fast diffusion pathway

Air spaces inside of leaf have a very large SA compared to volume of living tissue

There’s no specific transport system for gases —> they simply moving in through diffusion
Most gas exchange occurs in the leaf (which is specialised for gas exchange)

The leaf is specialised because it has:

• many pores (stomata) and so no cell is far from a stomata and therefore the diffusion pathway is short
• Numerous interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
• Large SA of mesophyll cells for rapid diffusion

Question 15

What are the adaptations that insects have in order to reduce water loss

Answer 15

Small SA:Vol (minimises the area over which water is lost)
Waterproof covering over their body surface (e.g. insects have a rigid outer skeleton of chitin that is covered with a waterproof cuticle)
Spiracles (they’re the openings of the tracheae at the body surface, they open/close to reduce water loss. Because it conflicts with the need for oxygen —> closes when insect is at rest)

Question 16

How do plants limit water loss

Answer 16

waterproof covering over parts of the leaves
The ability to open/close stomata when necessary
Xerophytic plants have also evolved to have a range of adaptations to limit water loss through transpiration

Question 17

What are xerophytes

Answer 17

plants that are adapted to living in areas where water is in short supply
Without these adaptations, they’d become desiccated and die

Question 18

What are some of the modifications in the leaves of xerophytes in order to reduce water loss by evaporation

Answer 18

A thick cuticle
Rolling up of leaves
Hair leaves
Stomata in the pits or grooves
A reduced SA:Vol of the leaves

Question 19

why does the body require a constant supply of oxygen and a constant removal of CO2

Answer 19

requires the oxygen in order to release ATP for respiration
the CO2 produced from respiration then needs to be removed because a build up can be harmful for the body

Question 20

what is the function of the ribcage

Answer 20

support and protect the lungs
the ribs can be moved by muscles between them

Question 21

what are the main components of the human gas-exchange system

Answer 21

lungs
trachea
bronchi
bronchioles
alveoli

Question 22

what is the structure + function of the lungs

Answer 22

the lungs are a pair of lobed structures made up of a series of highly branched tubules, called bronchioles, which end in tiny air sacs called alveoli

Question 23

what is the structure + function of trachea

Answer 23

the trachea is a flexible airway that is supported by rings of cartilage
the cartilage prevents the trachea collapsing as the air pressure inside falls when breathing in
the tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells

Question 24

what is the structure + function of bronchi

Answer 24

the bronchi are 2 divisions of the trachea, each leading to 1 lung
they’re similar in structure to the trachea and (like the trachea) also produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat
the larger bronchi are supported by cartilage, although the amount of cartilage is reduced as the bronchi gets smaller

Question 25

what is the structure + function of the bronchioles

Answer 25

they’re a series of branching subdivisions of the bronchi
their walls are made of muscle lined with epithelial cells
this muscle allows them to constrict so that they can control the flow of air in and out of the alveoli

Question 26

what is the structure + function of the alveoli

Answer 26

they’re minute air-sacs at the end of the bronchioles (with a diameter of between 100 and 300 micrometres)
between the alveoli there are some collagen and elastic fibres
the alveoli are lined with epithelium
the elastic fibres allow the alveoli to stretches they fill with air when breathing in
they then spring back during breathing out in order to expel the carbon dioxide-rich air
the alveolar membrane is the gas-exchange surface

Question 27

what is the definition of digestion

Answer 27

Digestion: The process in which large molecules are hydrolysed into small molecules which can be absorbed and assimilated

Question 28

What is physical breakdown and where does this process take place

Answer 28

Breaking large pieces into smaller ones

Mouth - teeth
stomach – muscular churning

Provides greater SA for chemical digestion

Question 29

What is chemical breakdown and where does this process take place

Answer 29

Enzymes hydrolyse large insoluble molecules into smaller soluble ones

All work through Hydrolysis reactions (adding water to break a bond)

Carbohydrases – carbohydrates into monosaccharides
Lipases – lipids into fatty acids & glycerol
Proteases – proteins into amino acids

Question 30

How are carbohydrates digested in the entire body (starch)

Answer 30

Mouth:
1) Amylase in saliva is mixed during chewing. Also contains mineral salts to maintain neutral pH (optimum for salivary amylase)
2) Salivary amylase starts hydrolysing starch into maltose

Stomach:
3) Salivary amylase is denatured due to HCl

Ileum:
4) Pancreatic juices from the pancreas are secreted into the ileum. These contain pancreatic amylase
5) Mineral salts are produced in by the pancreas & the intestinal wall to maintain a neural pH
6) Pancreatic amylase hydrolyses any remaining starch into maltose
7) Maltase is produced from the epithelial lining. This is part of the cell surface membrane & not free in the lumen. It is a membrane-bound disaccharidase.
8) Maltase hydrolyses maltose into α glucose.

Question 31

What other carbohydrates are digested and what enzymes are involved in their digestion

Answer 31

Sucrase –> sucrose to glucose & fructose
Lactase –> lactose to glucose & galactose

Question 32

What are the enzymes involved in protein digestion

Answer 32

Endopeptidases
Hydrolyse peptide bonds in the middle region of the protein molecule creating several peptide molecules

Exopeptidases
Hydrolyse peptide bonds on the terminal (end) amino acids releasing dipeptides & single amino acids

Dipeptidases
Hydrolyse the peptides bone between 2 amino acids (dipeptide) Membrane bound on the membrane of the ileum

Question 33

What are the steps in the digestion of lipids in to the lacteals

Answer 33

1.Lipase digests micelles and releases monoglycerides and fatty acids at the epithelial membrane to be absorbed by simple diffusion
2. Triglycerides are reformed in the SER
3. The Golgi produces chylomicrons from triglycerides and lipoproteins
4. The chylomicrons are exported by exocytosis
5. Chylomicrons are absorbed into the lacteals in the villi

Question 34

Describe the role of micelles in the absorption of fats into the cells lining the ileum.

Answer 34

1.Micelles include bile salts and fatty acids
2.Make the fatty acids (more) soluble in water;
3.Bring/release/carry fatty acids to cell/lining (of the ileum);
4.Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
5.Fatty acids (absorbed) bydiffusion;

Question 35

contractions of muscles during ventilation

Answer 35

Question 36

which intercostal muscles are involved in inhalation and which for exhalation

Answer 36

external intercostal muscles - inspiration
internal intercostal muscles - expiration

Question 37

what is the equation for pulmonary ventilation

Answer 37

tidal volume (dm^3) X ventilation rate (min^-1)