3A - Exchange and Transport Systems Flashcards
How easily an organism can exchange substances with the environment depends on what?
The organism’s surface area to volume ratio.
Give three substances an organism needs to exchange with its environment
1) Cells need to take up oxygen (for aerobic respiration) and nutrients
2) They also need to excrete waste products like carbon dioxide and urea
3) Most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too.
A mouse has a bigger surface area relative to its volume. Sketch a quick mathematical model to prove this.
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Explain how single-celled organisms exchange substances with the environment
In single-celled organisms, these substances can diffuse directly into (or out of) the cell across the cell-surface membrane. The diffusion rate is quick because of the small distances the substances would have to travel.
Explain why diffusion across the outer membrane in multicellular organisms is too slow. (2 reasons)
In multi-cellular organisms/animals diffusion across the outer membrane is too slow, for two reasons:
- Some cells are deep within the body - there’s a big distance between them and the outside environment
- Larger animals have a low surface area to volume ratio - it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.
What substances does an organism need to supply and remove from every one of its cells?
An organism needs to supply every one of its cells with substances like glucose and oxygen (for respiration).
It also needs to remove waste products from every cell to avoid damaging itself.
Multicellular animals cannot use straightforward diffusion to absorb and excrete substances, what do they use instead? (brief)
Specialised exchange organs
Briefly define mass transport
multicellular organisms need an efficient system to carry substances to and from their individual cells, this is mass transport.
In mammals, what does ‘mass transport’ usually refer to? Explain why.
The circulatory system. It uses blood to carry glucose and oxygen around the body. It also carries hormones, antibodies and waste like CO2.
What does mass transport in plants involve?
Mass transport in plants involves the transport of water and solutes in the xylem and phloem.
What two things can ‘metabolic activity’ inside cells do?
- Create waste products that need to be transported away
- Creates heat
How does size affect heat exchange?
The rate of heat loss from an organism depends on its surface area. If an organism has a large volume, e.g. Hippo, it’s surface area is relatively small. This makes it harder for it to lose heat from its body. If an organism is small, e.g. a mouse, its relative surface area is large, so heat is lost more easily. This means smaller organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm.
How does shape affect heat exchange?
Animals with a compact shape have a small surface area relative to their volume - minimising heat loss from their surface.
Animals with a less compact shape, (those that are a bit gangly or have sticky outy bits) have a larger surface area relative to their volume - this increases heat loss from their surface.
Whether an animal is compact or not depends on the temperature of their environment. Give three examples of animals that live in different environments, (including the temperatures).
-Arctic Fox
Body Temperature: 37 degrees celcius
Average Outside Temperature: 0 degrees celcius
The arctic fox has small ears and a round head to reduce its surface area to volume ratio and reduce heat loss.
-African Bat-Eared Fox
Body Temperature: 37 degrees celcius
Average Outside Temperature: 25 degrees celcius
The African Bat-Eared Fox has large ears and a more pointed nose to increase its surface area to volume ratio and increase heat loss
-European Fox
Body Temperature: 37 degrees celcius
Average Outside Temperature: 12 degrees celcius
The European Fox is an intermediate between the two, matching the temperature of its environment.
What are the two types of adaptations organisms have to aid exchange?
Behavioural and Physiological adaptations
Explain the adaptations SMALL desert animals may have.
Small= high surface area to volume ratio. This means they tend to lose more water as it evaporates from their surface. Some small dessert animals have kidney structure adaptations so that they produce less urine to compensate for the water loss.
Explain the adaptations small mammals living in cold regions may have.
Small mammals living in cold regions will have high metabolic rates. This means they need to eat large amounts of high energy foods such as seeds and nuts
Give examples of a behavioural, structural and physiological adaptations
When baboons on certain Indonesian islands discovered a variety of sweet potato growing in sandy soil, they learned to wash the root in water to remove the sand. That was a behavioral adaptation; they had not previously washed their foods.
A certain species of bird ate insect larvae that lived in trees. The species evolved a long, narrow beak to more easily reach its foods. That was a structural adaptation.
A group of white-skinned European humans migrated into Africa several thousand years ago. Over the course of many generations they evolved skin as dark as the native Africans. Dark skin is a response to the intense sun. That was a physiological adaptation.
Explain the adaptations a smaller mammal may have, for when the weather gets really cold.
Smaller mammals have thick layers of fur or hibernate when the weather gets really cold.
Explain the adaptations a larger organism living in hot regions may have. (Give examples of these organisms)
E.g. Hippos and elephants
They find it hard to keep cool as their heat loss is relatively slow. Elephants have developed large flat ears to increase their surface area, allowing them to lose more heat. Hippos spend much of the day in the water - a behavioural adaptation to help them lose heat.
Explain why a small mammal needs a relatively high metabolic rate compared to a large mammal
A small mammal has a bigger surface area to volume ratio than a large mammal
This means that heat is lost more easily from a small mammal
So a smaller mammal needs a relatively high metabolic rate, in order to generate enough heat to maintain a constant body temperature.
Gas exchange surfaces have two major adaptations. What are they?
1) They have a large surface area
2) They’re thin, (often just one layer of epithelial cells)- this provides a short diffusion pathway across the gas exchange surface.
What does an organism have to maintain for effective gas exchange?
The organism has to maintain a steep concentration gradient of gases across the exchange surface.
How do single-celled organisms exchange gases?
-Single-celled organisms absorb and release gases by diffusion through their outer surface..
Why is there no need for single-celled organisms to have a gas exchange system?
They have a relatively large surface area, a thin surface and a short diffusion distance pathway.
(so basically, oxygen can take part in biochemical reactions as soon as it diffuses into the cell, therefore there is no need for gas exchange system).
What do fish use for gas exchange?
A counter-current gas exchange system
Explain why fish need a counter-current exchange system
There’s a lower concentration of oxygen in water than in air. So fish need special adaptations to get enough of it.
Explain how a counter-current gas exchange system works in fish.
- Water, containing oxygen, enters the fish through its mouth and passes out through the gills.
- Each gill is made of lots of thin plates called gill filaments, which give a big surface area for exchange of gases.
- The gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more.
- The lamellae have lots of blood capillaries and a thing surface layer of cells to speed up diffusion.
- Blood flows through the lamellae in one direction and water flows over in the opposite direction. This is called a counter-current system. It maintains a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.
Draw a diagram explaining how a counter-current exchange system works in fish.
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What are lamellae?
the tiny structures that cover the gill filaments
Draw a diagram of one gill.
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What do insects use to exchange gases?
Tracheae
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Explain how insects use tracheae to exchange gases
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- Insects have microscopic air-filled pipes called tracheae which they use for gas exchange
- Air moves into the tracheae through the pores on the surface called spiracles
- Oxygen travels down the concentration gradient towards the cells
- The tracheae branch off into smaller tracheoles which have thin, permeable walls and go into individual cells. This means that oxygen diffuses directly into the respiring cells - the insect’s circulatory system doesn’t transport O2.
- Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
- Insects use rhythmic abdominal movements to move air in and out of the spiracles.
Why do insects use rhythmic abdominal movements?
To move air in and out of the spiracles
What are spiracles?
Pores on the surface of an insect
What is a dicotyledonous plant?
- One with more than three flowers in a bunch
- Veins on leaves tend to be net-like rather than straight up and down
How do dicotyledonous plants exchange gases?
At the surface of the mesophyll cells
Explain how dicotyledonous plants exchange gases with the environment
- Plants need CO2 for photosynthesis, which produces O2 as a waste gas. They need O2 for respiration, which produces CO2 as a waste gas.
- The main gas exchange surface is the surface of the mesophyll cells in the leaf. They’re well adapted for their function - they have a large surface area.
- The mesophyll cells are inside the leaf. Gases move in and out through special pores in the epidermis called stomata. (singular = stoma)
- The stomata can open to allow exchange of gases, and close if the plant is losing too much water. Guard cells control the opening and closing of stomata.
In plants, what do guard cells control?
The opening and closing of stomata
In plants, what is the main gas exchange surface?
The surface of the mesophyll cells in the leaf.
What are stomata and where are they found?
Stomata are special pores in the epidermis
Draw a diagram of the structure of a leaf cell with labels.
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How have insects adapted (evolved) to minimise water loss?
If insects are losing too much water, they close their spiracles using muscles. They also have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which minimize evaporation.
