Topic 3 - organisms exchange substances

Question 1

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into the lymph vessels

Answer 1

1. Micelles contain bile salts and fatty acids/monoglycerides
2. Make FA’s more soluble in water / bring them to the cell lining (of the ileum) / maintain a higher conc of FA’s at cell
3. FA’s absorbed by diffusion
4. Triglycerides reformed in cells
5. Vesicles move to the cell membrane

Question 2

The movement of Na+ out of the cell allows the absorption of glucose into the cell lining of the ileum. Explain how

Answer 2

Generates a conc gradient for Na+
Na+ moves in by facilitated diffusion, brings glucose with it

Question 3

Describe the role of micelles in the absorption of fats into the cell lining of the ileum

Answer 3

Include bile salts and fatty acids
Make fatty acids more soluble in water
Bring/release FA’s to the cell lining
Maintain a higher conc of FA’s at the cell lining
FA’s are absorbed by diffusion

Question 4

Explain the importance of the Golgi Body i the absorption of lipids

Answer 4

Modifies triglycerides
Combines triglycerides with proteins
Forms vesicles

Question 5

The mass flow hypothesis is used to explain the movement of substances through the phloem. Explain how pressure is generated inside this phloem tube

Answer 5

Sucrose is actively transported into the phloem
Lowering the water potential
Water moves into the phloem by osmosis

Question 6

Describe the cohesion-tension theory of water transport in the xylem

Answer 6

Water lost from leaf due to transpiration/evaporation of water from leaf cells
Lowers water potential of mesophyll/leaf cells
Water pulled up xylem
Water molecules ‘stick’ together by hydrogen bonds
Forms continuous columns of water
Adhesion of water to walls of xylem

Question 7

Describe the mass flow hypothesis for the mechanisms if translocation in plants

Answer 7

In the source sugars actively transported into phloem
By companion cells
Lowers water potential of sieve cells
Increase in pressure causes mass movement (towards the sink)
Sugars used/converted in root for respiration, for storage

Question 8

Describe and explain one feature of the alveolar epithelium that makes them adapted for gas exchange

Answer 8

Flattened cells/single layer of cells - one cell thick
Reduced diffusion distance
Permeable
Allows diffusion of O2/CO2

Question 9

Describe and explain the mechanism that causes lungs to ill with air

Answer 9

Diaphragm contracts and external intercostal muscles contract
(causes vol to decrease) pressure decreases
Air moves down a pressure gradient

Question 10

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill

Answer 10

Water and blood flow in opposite directions
Maintains a conc gradient of O2
Along the whole length of the lamella

Question 11

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

Answer 11

Across the alveolar epithelium
Endothelial of the capillary

Question 12

Explain how one feature of an alveolus allows for efficient gas exchange to occur

Answer 12

One cell thick
Creating a short diffusion pathway

Question 13

Describe the gross structure of the human gas exchange system and how we breathe in and out

Answer 13

Trachea, bronchi, bronchioles, alveoli
IN: diaphragm contracts and external intercostal muscles contract
Vol increases and pressure decreases in thoracic cavity
OUT: diaphragm relaxes and internal intercostal muscles contract

Question 14

Explain 3 ways in which an insect’s tracheal system is adapted for efficient gas exchange

Answer 14

Tracheoles have thin walls so short diffusion distance
Highly branches so short diffusion distance to cells / large surface area
Trachea provide tubes full of air so fast diffusion

Question 15

Explain two ways in which the structure of fish gills is adapted for efficient gas exchange

Answer 15

Lots of lamella so a large surface area
Thin so short diffusion pathway

Question 16

Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills

Answer 16

Water and blood flow in opposite directions
Blood always passing water with a high conc of O2
Diffusion gradient is maintained throughout the whole length of the lamella

Question 17

Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs

Answer 17

Renal vein
Vena cava to right atrium
Right ventricle to pulmonary artery

Question 18

Tissue fluid is formed from blood at the arteriole end of a capillary bed
Explain how water from tissue fluid is returned to the circulatory system

Answer 18

(Plasma) proteins remain
Causes water potential gradient/ reduces it
Water moves (to blood) via osmosis
Returns (to blood) by lymphatic system

Question 19

Explain how an arteriole can reduce the blood flow into capillaries

Answer 19

Muscle contracts
Constricts/narrows arteriole/lumen

Question 20

Describe the advantage of the Bohr effect during intense exercise

Answer 20

Increase dissociation of oxygen
For aerobic respiration at the tissues/muscles/cells

Question 21

Structure of a leaf

Answer 21

(Waxy) cuticle
upper epidermis
palisade mesophyll cells
spongy mesophyll
sub-stomatal air space
lower epidermis

Question 22

Phloem pressure is reduced during the hottest part of the day. Use your knowledge of transpiration and mass flow to explain why

Answer 22

Increase in transpiration
Water is lost via the stomata
Less water moves from the xylem to the phloem

Question 23

Describe how the structure of glycogen is related to its function

Answer 23

1. Helix/coiled/branched so compact;

Accept description of ‘compact’, eg many glucoses packed closely/densely/tightly

2. Polymer of glucose so easily hydrolysed;
3. Branched so more ends for faster hydrolysis;
4. Glucose (polymer) so provides respiratory substrate for energy (release);
5. Insoluble so not (easily) lost (from cell)

OR

Insoluble so does not affect water potential/osmosis