Topic 3A - Exchange And Transport Systems Flashcards
Describe why organisms should exchange substances with their environment.
Cells need to take in oxygen for aerobic respiration, and nutrients. Excrete waste products like carbon dioxide and urea. To stay at the same temperature, heat needs to be exchanged.
Which animals have a higher SA:V ratio
Smaller.
What’s the difference between single-celled organisms and multicellular animals.
In single-celled organisms, substances such as glucose and oxygen (for respiration) can diffuse directly into the cell across the cell-surface membrane, because the diffusion rate is quick and the distance is small.
In multicellular animals, diffusion is too slow because the cells are deep within the body, making distances large. Also larger animals have lower SA:V ratio. Therefore they need exchange organs (like lungs).
What is the system animals use to carry substances to and from cells.
Mass transport. In mammals, usually referring to the circulatory system using blood. This carries glucose, oxygen, hormones, antibodies, and waste like CO2.
How does size affect heat exchange?
If an organism has a large volume, it’s surface area is relatively small. This makes it harder to lose heat from its body. If an organism is small, it’s relative surface area is large, so heat is lost more easily. Therefore smaller organisms need a high metabolic rate 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 which minimises heat loss from their surface. Animals with a less compact shape have a larger surface area relative to their volume, increasing heat loss from their surface. The arctic fox has small ears and a round head to reduce SA:V ratio and heat loss. The African fox has large ears and a more pointed nose to increase SA:V ratio and heat loss.
What are some behavioural and psychological adaptions to aid exchange?
Animals with a high SA:V ratio lose more water as it evaporates from their surface. Some small desert mammals have kidney structure adaptations so they produce less urine to compensate. Small mammals living in cold regions need to eat lots of high energy foods to support their high metabolic rate. Smaller mammals may have thick layers of fur or hibernate when the weather gets cold. Larger organisms living in hot regions find it hard to keep cool as their heat loss is slow. Elephants developed large flat ears to increase their surface area, so they can can lose more heat. Hippos spend a lot of time in the water so that they lose heat.
What adaptations do gas exchange surfaces have?
Large surface area. Thin (one layer of epithelial cells) to provide a short diffusion pathway across the gas exchange surface. Organism maintains a steep concentration gradients of gases across the exchange surface.
Why don’t single-celled organisms have a gas exchange system.
They absorb and release gases by diffusion through their outer surface.
Describe the gas exchange system in fish.
There’s a lower concentration of oxygen in water than in air. Water enters the fish through its mouth and passes out through the gills. Each gill is made up of thin plates called gill filaments, which give a big surface area. The gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area more. The lamellae have lots of blood capillaries and a thin surface layer of cells.
What is the counter-current system?
Blood flows through the lamellae in one direction and water flows in the opposite direction. This maintains a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than in the blood.
How do insects exchange gases?
Insects have microscopic air-filled pipes called tracheae. Air moves into the trachea through pores on the surface called spiracles. Oxygen travels down the concentration gradient towards the cells. The tracheae branch off into smaller tracheoles which increases surface area. These have thin, permeable walls and go to individual cells. Therefore the oxygen diffuses directly into respiring cells, and the insect circulatory system doesn’t transport O2. Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles. Insects use rhythmic abdominal movements to move air in and out of the spiracles.
How do dicotyledonous plants exchange gases?
Plants need CO2 for photosynthesis, producing O2 as a waste gas. They need O2 for respiration, producing CO2 as a waste gas. The main gas exchange surface is the surface of the mesophyll cells in the leaf, which have a large surface area. The mesophyll cells are inside the leaf. Gases move in and out through pores in the epidermis called stomata. Guard cells control the opening and closing of them.
Exchanging gases can make you lose water. What adaptations minimise this?
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 which reduce evaporation. Plants stomata are kept open in the day to allow gaseous exchange. Water enters the guard cells making them turgid, but turn flaccid when needing to close the pore.
What is a xerophyte? What are their adaptations?
Plants in very warm, dry, or windy habitats. Adaptations include stomata sink in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air, reducing water diffusion. Hairs on the epidermis trap moist air around the stomata. Curled leaves with stomata inside protect them from windy conditions that increase diffusion and evaporation. Fewer stomata, so fewer places for water to escape. Waxy, waterproof cuticles on leaves and stems to reduce evaporation.
What is the structure of the human gas exchange system?
As you breathe in, air enters the trachea. The trachea splits into two bronchi, each leading to a lung. Each bronchus branches off into smaller tubes called bronchioles. The bronchioles end in alveoli.
What happens in inspiration?
External intercostal and diaphragm muscles contract. This causes the rib cage to move upwards and outwards, and the diaphragm to flatten, increasing the volume of the thoracic cavity (space where the lungs are). As the volume of the thoracic cavity increases, pressure decreases. Since air flows from an area of high pressure to low pressure, air flows down the trachea into the lungs. Inspiration is active and requires energy.
What happens during expiration?
The external intercostal and diaphragm muscles relax. The ribcage moves downwards and inwards and the diaphragm becomes curved again. The volume of the thoracic cavity decreases, causing air pressure to increase, so air is forced down the pressure gradient out of the lungs. Expiration is passive. Expiration can be forced. During forced expiration, the external intercostal muscle relax and the internal intercostal muscles contract, pulling the ribcage further down and in.
How does gaseous exchange happen in the alveoli?
Each alveolus is made from a single layer of thin, flat cells called alveolar epithelium. Lots of alveoli mean large surface area. Alveoli are surrounded by a network of capillaries. O2 diffuses out of the alveoli, across the alveolar epithelium and capillary epithelium, into the haemoglobin in the blood. CO2 diffuses into the alveoli from the blood and is breathed out.
