Biology AS Chapter 6 - Exchange Flashcards
What are 5 examples of things that need to be interchanged between organisms and their environment?
- Respiratory gases
- Nutrients
- Vitamins
- Excretory products
- Heat
What are two examples of ways organisms have evolved to allow efficient exchange of gases?
- A flattened shape so no cell is ever far from the surface
- Specialised exchange surfaces with large areas to increase the surface area to volume ratio (eg lungs and gills)
What 5 characteristics must specialised exchange surfaces have to allow effective transfer of materials?
- A large surface area relative to the volume of the organism
- Very thin so the diffusion distance is short
- Selectively permeable
- Movement of the environmental medium to maintain a diffusion gradient
- A transport system to ensure the movement of the internal medium to maintain a diffusion gradient
Why are specialised exchange surfaces usually located inside an organism?
For protection because they are thin so can be easily damaged and dehydrated
Describe the respiratory system of an insect
They have an internal network of tubes called tracheae which are supported by strengthened rings to prevent them from collapsing. These divide into smaller dead-end tubes called tracheoles which extend throughout the tissues of the insect, allowing oxygen to be brought directly to respiring tissues
What are the 3 ways respiratory gases move in and out of the tracheal system in insects?
- Along a diffusion gradient
- Mass transport –> muscle contraction can squeeze the trachea, enabling mass movements of air in and out
- The ends of the tracheoles are filled with water –> lactate is produced during respiration, decreasing water potential and so the water moves into the cells by osmosis. This decreases the volume in the tracheoles and so draws air into them
How do gases enter and leave the tracheae in insects?
Through tiny pores called spiracles
What is a disadvantage of the tracheal system in insects?
It relies mostly on diffusion and so pathways have to be short, thereby limiting the insects size
Describe the countercurrent exchange principle in fish
- Blood that is already well loaded with oxygen meets water which has its max concentration of oxygen and so diffusion of oxygen from the water into the blood occurs
- Blood with little oxygen in it meets water which has had most of its oxygen removed and so oxygen enters the blood via diffusion
- This is due to blood and water flowing in opposite directions and so about 80% of the oxygen available in the water is absorbed into the blood, compared to only 50% if they flow in the same direction
What 3 adaptations do the leaves have to allow for rapid diffusion?
- Many small pores, called stomata, and so no cell is far from one and the diffusion pathway is short
- Numerous interconnecting air-spaces that occur throughout the mesophyll so gases readily come into contact with mesophyll cells
- Large surface area of mesophyll cells for rapid diffusion
How is the rate of gaseous exchange in plants controlled?
Each stoma (singular of stomata) is surrounded by guard cells which can open and close the stomatal pore, controlling the rate
What adaptations do insects have to reduce water loss?
- Small surface area to volume ratio –> minimise the area over which water is lost
- Waterproof coverings –> their covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle
- Spiracles –> able to open and close to control water loss
How do plants limit water loss?
- Waterproof coverings
- Ability to close stomata
What are xerophytes?
Plants that are adapted to living in areas where water is in short supply
How are xerophytes adapted to limit water loss?
- Thick cuticle –> less water can escape
- Rolling up of leaves –> traps a region of air which becomes saturated with water vapour and has a very high water potential. There is no gradient and so no water is lost
- Hairy leaves –> traps moist air and so the water potential gradient is reduced and less is lost
- Stomata in pits or grooves –> trap moist air and reduce the water potential gradient so less is lost
- Reduced surface area to volume ratio of leaves –> slower rate of diffusion so water loss is reduced
Why are the lungs located inside the body?
- Air is not dense enough to support and protect them
- The body would otherwise lose a great deal of water and dry out
Describe the structure of the lungs, starting at the trachea
The trachea divides into 2 tubes called the bronchi, each leading to one lung. These then divide into bronchioles and then into alveoli which is where gaseous exchange occurs
How do bronchioles control the flow of air in and out of the alveoli?
Their walls are made up of muscle lined with epithelial cells and this muscle allows them to constrict, thereby controlling the flow of air
What are the two types of intercostal muscles and how do they differ?
- Internal intercostal muscles –> contraction leads to expiration
- External intercostal muscles –> contraction leads to inspiration
Describe the process of inspiration (expiration is just the opposite)
- The external intercostal muscles contract, while the internal intercostal muscles relax
- The ribs are pulled upwards and outwards, increasing the volume of the thorax
- The diaphragm contracts and flattens, increasing the volume of the thorax
- The increased volume of the thorax results in a reduction of pressure in the lungs
- Atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs
Why is diffusion between the alveoli and the blood very rapid?
- Red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
- The distance between the alveoli and the red blood cells is reduced as the red blood cells are flattened against the capillary walls
- The walls of alveoli are very thin (one cell) so there is a short diffusion distance
- Alveoli and pulmonary capillaries have a large total surface area
- Steep concentration gradient is always maintained
What is the structure and role of the stomach?
A muscular sac with an inner layer which produces enzymes. Its role is to store and digest food, especially proteins, and it has glands which produce enzymes to digest these proteins
What is the structure and role of the ileum?
It is a long muscular tube. Food is further digested here by enzymes which are produced by its walls and by glands which pour their secretions into it
How is the ileum adapted to its function of digesting food?
The inner walls are folded into villi which gives them a large surface area. These then have millions of tiny projections called microvilli on the epithelial cells of each villus, further increasing the surface area
