Organisms exchange Surfaces Unit 3

Question 1

whats the total oxygen requirement correlated to and the rate of absorption of gases by an organism

Answer 1

oxygen- correlated to its total volume. the bigger the organism the more oxygen it requires. - larger/ more cells therefore requiring more energy for cellular processes
the rate of absorption of gases by an organism is correlated to the size of its SA

Question 2

What does the sa:v show

Answer 2

Shows the relationship between the size of the surface area and the size of the volume
Both values must the ‘same’ units
Volume is always at 1 - this allows direct comparison between organisms of different sizes.

Question 3

How do Single-celled organisms/ small organisms exchange gases across their body surface:

Answer 3

Single-cellular organisms exchange materials by diffusion on their surface w their environment
They have a short diffusion pathway as they are small
A large SA:Vol ratio due to their small volume compared to the surface area of their cell surface membrane.

Question 4

Multi-cellular/ larger organisms exchange gases across their body surface.

Answer 4

Larger organisms have lower surface area to volume ratio:
• Diffusion is too slow as some cells are deep within the body
• A large volume of animal has requirements too high for the available surface area

Question 5

What have large/ multicellular organisms done to overcome slow diffusion

Answer 5

To overcome this, organisms have developed adaptations.
1. Some organisms have evolved to have a body shape which maximises their surface area. E.g by being flattened or elongated.
2. Some organisms have developed specialised exchange organs and delivery systems to maximise gas exchange and transport For example, gills in fish and amphibians, and lungs in mammals, increase surface area for exchange
• Gills are folded into lamella
• Lungs are folded into alveoli
The oxygen diffuses into the circulatory system (mass transport) to deliver gases directly to cells.
Insects, meanwhile, have developed tracheal systems. Which are series of specialised tubes in direct contact with cells. They also maintain a small size to maintain a short diffusion distance.

Question 6

Surface area: volume and heat loss in smaller animals and adaptations

Answer 6

Smaller animals have a larger surface area to volume ratio compared to larger animals. This means that More heat loss per gram/in relation to body size by radiation compared to larger animals.In order to maintain a constant body temperature, smaller animals have a higher metabolic rate per gram of body mass so (Faster rate of) respiration and These chemical reactions release heat which is used to maintain body heat.
Adaptations for heat loss
Organisms that live areas of high temperatures tend to have adaptations to enable them to stay cool.
These adaptations increase their surface area: volume ratio and can include a smaller body size (compared
to similar species in cooler climates), larger ears, longer faces and longer noses.
Organisms that live in areas of cold temperatures are adapted to reduce their surface area: volume ratio,
this decreases the loss of heat via radiation and helps maintain their internal body temperature.
Adaptations can be: a larger body size, smaller ears, and compact facial features.

Question 7

units in order of largerst and how to convert eg m, dm

Answer 7

( M. )
x10 ( dm ) div by 10
x10 ( cm ) div by 10
x10 ( mm) div by 10
x1000 ( ųm ) div by 1000
x1000 ( nm ) div by 1000

Question 8

Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. 3marks

Answer 8

Mouse:
(Smaller so) larger surface area to volume ratio;
More heat loss (per gram/in relation to body size);
(Faster rate of) respiration

Question 9

Describe how gas exchange occurs in Single-celled organisms and large organisms:

Answer 9

Single-celled organisms exchange gases across their body surface by diffusion:
• They have a large surface area to volume ratio and a short diffusion pathway
Large organisms have specialised gas exchange surfaces:
They have a large surface area for diffusion
Thin surface, so short diffusion pathway
Maintenance of a steep diffusion gradient

Question 10

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake.

Answer 10

1. Larger organisms have a smaller surface area:volume (ratio)
   2.Overcomes long diffusion pathway

Question 11

Describe The tracheal system and gas exchange in an insect

Answer 11

Insects have a branched, chitin-lined system of tracheae with openings called spiracles.
Oxygen diffuses in, down a concentration gradient, through the open spiracles and into tubes called tracheae. The tracheae are lined with rings of chitin to prevent them from collapsing during ventilation.
The trachee split into many branches called tracheoles.
oxygen diffuses directly into the respiring cells so no blood’s required
The tracheoles are not lined with chitin and so are permeable - this makes them the site of gas exchange in insects.

Question 12

Features of gas exchange in insects:

Answer 12

Short diffusion path
• Tracheoles are in direct contact with (and sometimes enter them) the insects body cells.
• Insects are small maintaining an overall short diffusion pathway from spiracles to respiring tissues.
• The walls of the tracheoles are thin.

Concentration gradient:
• The cells respire using the oxygen so the concentration of oxygen at the cells remains low.
• Body can be moved by muscles to move air so maintains concentration gradient for oxygen and carbon dioxide.

Large surface area:
• Tracheoles are very branched.

Question 13

Describe how insects are evolved to prevent water loss

Answer 13

Preventing Water loss:
Insects are coated in an exoskeleton that is made out of chitin - this is impermeable so reduces the loss of water by evaporation from the insects tissues. To aid this the exoskeleton is also covered in a waxy cuticle
which is also impermeable/waterproof.
When the spericlss are open water vapour can diffuse out of them - to reduce this loss spiracles are lined by hairs which trap the water vapour around the spiracle. This reduces the water potential gradient so less water is lost. Insects can also close the spiracles to further prevent the loss
of water.

Question 14

Describe how an insects able to obtain oxygen and limit water loss (6 marks)

Answer 14

Air enters through spiracles through trachea. Creates diffusion gradient in trachea.
oxygen diffuses into the cells
Body covered with waxy cuticle
spericals able to close reducing water loss

Question 15

what happens to tracheoles during exercise

Answer 15

Fluid in the end of tracheoles moves into tissues during exercise.
• Cells produce lactate by anaerobic respiration.
• Reduces water potential.
• Water moves in down W gradient by osmosis.
• Increases volume in tracheoles and reduces pressure to draw more in.
• Diffusion through air is faster.

Question 16

How have fishes adapted for efficient exchange of gases and why

Answer 16

Water has a lower oxygen content than air, and diffusion rates are slower in water than air. This means that fish have developed a very efficient method of gas exchange to meet their oxygen demand.
Fish exchange gases at the gills.
Short diffusion pathway:
* Gills have a single layer of epithelial cells and the capillaries within the gills have a single layer of endothelial cells.
Large surface area:
* The gills are folded into filaments, and these are further folded into lamellae.
Concentration gradient:
* The gills have lots of blood capillaries.
* Blood in the capillaries flows in the opposite direction to the flow of water over the gills - this is called counter current flow.

Question 17

What’s counter current flow in fish and how’s oxygen diffused

Answer 17

Counter current flow: water and blood flow in opposite directions so maintains diffusion along length of lamella
Diffusion of oxygen
There is a diffusion gradient favouring
the diffusion of oxygen from water
into the blood all the way across the
gill lamellae, Almost all the oxygen
from the water diffuses into the blood.

Question 18

How does co2 enter leafs and where does gas exchange occur

Answer 18

Plants need CO2 For photosynthesis and produce O2 as a waste gas.but they need it for respiration as plants respire all the time
Carbon dioxide diffuses into the leaves down a concentration gradient through pores in the surface of the leaf called stomata.
Gas exchange occurs at the surface of the mesophyll cells. The mesophyll ells are where most of the photosynthesis occurs - particularly the palisade mesophyll cells - their tall and long shape increases the surf -ace area for gas exchange.

Question 19

What do plants have to increase efficiency of gas exchange

Answer 19

Large surface area:
• Large, flat leaf
• Tall, long palisade mesophyll cells.
Short diffusion pathway:
• Thin leaf.
• Air spaces.
Concentration gradient:
• Mesophyll cells use the carbon dioxide, maintaining a low concentration at the mesophyll cells.
Stomata:
The stomata can open (to allow gasses through) and close (to reduce water loss)
The two guard cells control the opening/closing of stomata.

Question 20

How do plants reduce water loss

Answer 20

All plants can lose water through their stomata by diffusion/evaporation in a process called transpiration.
To reduce water loss most plants can do the following:
* Stomata can close when the guard cells lose water and become flaccid, further reducing water loss.
* The leaf is covered in a hydrophobic, waxy cuticle which reduces water loss from cells by evaporation.
* Most stomata are on the lower surface of the leaf, as this reduces the loss of water by evaporation out of the stomata.
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Question 21

Which types of plants can further reduce water loss:

Answer 21

• Xerophytes are plants adapted for hot and dry. conditions e.g. Marram grass
• Rolled leaf shape as upper epidermis is facing inwards
to trap humid air
• Reduced leaf surface area for transpiration
• Sunken stomata, humid air is trapped reducing water potential gradient between inside leaf and humid trapped air
No stomata on exposed lower surface
Hairs, trap moist air
Thick cuticle, waxy covering reduced evaporation

Question 22

Whys counter current so important in fishes and what is it

Answer 22

When water flows over the gills in the opposite direction to the flow of blood in the capillaries.
It ensures equilibrium is not reached and that diffusion gradient maintained across the entire length of gill lamella