Give an example of things cells exchange with their environment.
1. Cells need to be take in things like oxygen and glucose for aerobic respiration and other metabolic reactions. 2. They also need to excrete waste products from these reactions - like carbon dioxide and urea.
What determines how easy it is to exchange substances in an organism?
The organism's surface area to volume ratio determines how easy the exchange of substances is.
Prove mathematically that smaller animals have a bigger surface area to volume ratio.
If a hippo was a represented by a block measuring 2cm x 4cm x 4cm. The volume would be 32cm³ The surface are would be 64cm² Surface area:Volume ratio of 2:1 Compare this to a mouse block measuring 1cm x 1cm x 1cm. The volume would be 1cm³ The surface area would be 6cm² Surface area:Volume ratio of 6:1 The mouse has a higher surface area to volume ratio.
How can one calculate the Surface area:Volume ratio?
To calculate the surface area to volume ratio you just divide the surface area by the volume.
What's the equation for the volume of a sphere?
The equation for the volume of a sphere is ³/₄πr³.
How do single celled organisms exchange substances?
In single celled organisms, substances can diffuse directly into or out of the cell across the cell surface membrane. This diffusion rate is quick because of the small distances the substances have to travel.
Why is diffusion too slow for exchanging substances in multicellular animals?
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 an animal through a relatively small outer surface. Multicellular organisms have a higher metabolic rate than single celled organisms, so they can use up oxygen and glucose faster. So rather than using diffusion to absorb and excrete substances, multicellular animals need specialised exchange surfaces - like the alveoli in the lungs.
How do root hair cells help with exchanging substances?
Most exchange surfaces have a large surface area. 1. E.g. The cells on plant roots grow into long 'hairs' which stick out into the soil. Each branch of a root will be covered in millions of these microscopic hairs. 2. This gives the roots a large surface area, which helps to increase the rate of absorption of water (by osmosis) and mineral ions (by active transport) from the soil.
How do the alveoli help with exchanging substances?
Most exchange surfaces are thin. 1. The alveoli are the gas exchange surface in the lungs. 2. Each alveolus is made from a single layer of thin flat cells called the alveolar epithelium. 3. Oxygen diffuses out of the alveolar space into the blood. carbon dioxide diffuses in the opposite direction. 4. The thin alveolar epithelium helps to decrease the distance over which the oxygen and carbon dioxide diffusion takes place, which increases the rate of diffusion.
What do most exchange surfaces have a good supply of? Give examples.
They have a good blood supply and/or ventilation. E.g. Alveoli - The alveoli are surrounded by a large capillary network, giving each alveolus its own blood supply. The blood constantly takes oxygen away from the alveoli, and brings more carbon dioxide. The lungs are also ventilated so the air in each alveolus is constantly replaced. These features help to maintain the concentration gradients of oxygen and carbon dioxide. E.g. Fish Gills - The gills are the gas exchange surface in fish. In gills, oxygen and carbon dioxide are exchanged between the fish's blood and the surrounding water. Fish gills contain a large network of capillaries - this keeps them well supplied with blood. they're also well-ventilated as fresh water constantly passes over them. These features help to maintain a concentration gradient of oxygen - increasing the rate at which oxygen diffuses into the blood.
What are the gas exchange organs in mammals?
In mammals the gas exchange organs are the lungs.
Explain how gas exchange works within mammals.
1. As one breathes in, air enters the trachea (windpipe). 2. The trachea splits into two bronchi - one bronchus leading to each lung. 3. each bronchus then branches off into smaller tubes called bronchioles. 4. The bronchioles end in small 'air sacs' called alveoli where gases are exchanged. 5. The ribcage, intercostal muscles and diaphragm all work together to move air in and out.
What is the function of a goblet cell in mammalian gas exchange?
Goblet cells (lining the airways) secrete mucus. the mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.
What is the function of cilia in mammalian gas exchange?
Cilia (on the surface of the cells lining the airways) beat the mucus. This moves the mucus (plus the trapped microorganisms and dust) upward away from the alveoli toward the throat, where it's swallowed. this helps prevent lung infections.
What is the function of elastic fibres in mammalian gas exchange?
Elastic fibres in the walls of the trachea, bronchi, bronchioles and alveoli help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help the push the air out when exhaling.
What is the function of smooth muscle in mammalian gas exchange?
Smooth muscle in the walls of the trachea, bronchi and bronchioles allow their diameter to be controlled. During exercise the smooth muscle relaxes, making the tube wider. This means there's less resistance to airflow and air can move in and out of the lungs more easily.
What is the function of the rings of cartilage in mammalian gas exchange?
Rings of cartilage in the walls of the trachea and bronchi provide support. it's strong but flexible it stops the trachea and bronchi collapsing when you breathe in and the pressure drops.
Describe the constituent parts of the trachea.
The trachea has large C - shaped pieces of cartilage, smooth muscle, elastic fibres which surround the ciliated epithelium and goblet cells.
Describe the constituent parts of the bronchi.
The bronchi have smaller pieces of cartilage, smooth muscle, elastic fibres, goblet cells and a ciliated epithelium.
Describe the constituent parts of the larger bronchiole.
The larger bronchiole doesn't have any cartilage, has smooth muscle, elastic fibres, giblet cells and a ciliated epithelium.
Describe the constituent parts of the smaller bronchiole.
The smaller bronchiole has no cartilage, has smooth muscle, elastic fibres, no goblet cells and a ciliated epithelium.
Describe the constituent parts of the smallest bronchiole.
The smallest bronchiole have no cartilage, no smooth muscle, has elastic fibres, no goblet cells and no cilia.
Describe the constituent parts of the alveoli.
The alveoli have no cartilage, no smooth muscle, has elastic fibres, no goblet cells and no cilia.
What is ventilation in mammals?
Ventilation in mammals is breathing in and out.
What does ventilation consist of and how is it controlled?
Ventilation consists of inspiration (breathing in) and expiration (breathing out). It's controlled by the movement of the diaphragm, internal and external intercostal muscles and ribcage.
Explain what happens during inspiration.
1. The external intercostal and diaphragm muscles contract. 2. This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax (the space where the lungs are). 3. As the volume of the thorax increases the lung pressure decreases (to below atmospheric pressure). 4. This causes air to flow into the lungs. 5. Inspiration is an active process - it requires energy.
Explain what happens during expiration.
1. The external intercostal and diaphragm muscles relax. 2. The ribcage moves downwards and inwards snd the diaphragm becomes curved again. 3. The thorax volume decreases, causing air pressure to increase (to above atmospheric pressure). 4. Air is forced out of the lungs. 5. Normal expiration is a passive process - it doesn't require energy. 6. Expiration can be forced though (e.g. if you needed to blow out the candles on your birthday cake). During forced expiration, the internal intercostal muscles contract, to pull the ribcage down and in.
What is the tidal volume?
Tidal volume - The volume of air in each breath - usually about 0.4dm³.
What is the vital capacity?
Vital capacity - The maximum volume of air that can breathed in or out.
What is the breathing rate?
Breathing rate - Number of breaths taken per minute.
What is the oxygen consumption/oxygen uptake?
Oxygen consumption/uptake - The rate at which an organism uses up oxygen (e.g. number of dm³ per minute).
What is a spirometer?
A spirometer is a machine that can give readings of tidal volume, vital capacity, breathing rate and oxygen uptake.
How can a spirometer be used to investigate breathing?
1. A spirometer has an oxygen filled chamber with a movable lid. 2. The person breathes through a tube connected to the oxygen chamber. 3. As the person breathes in and out, the lid of the chamber moves up and down. 4. These movements can be recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace. Or the spirometer can be hooked up to a motion sensor - this will use the movements to produce electronic signals, which are picked up by the datat logger. 5. The soda lime in the tube the subjects breathes into absorbs carbon dioxide.
What happens to the total volume of gas in the chamber of the spirometer?
The total volume of gas in the chamber decreases over time. This is because the air that's breathed out is a mixture of oxygen and carbon dioxide. The carbon dioxide is absorbed by the soda lime - so there's only oxygen in the chamber which the subject inhales from. As this oxygen gets used up by respiration, the total volume decreases.
Give the adaptations that a fish has as a result of there being a lower concentration of oxygen in water than in air.
1. Water, containing oxygen, enters the fish through its mouth and passes out through the gills. 2. Each gill is made of lots of thin branches called gill filaments or primary lamellae, which give a big surface area for exchange of gasses. The gill filaments are covered in lots of tiny structures called the gill plates or secondary lamellae, which increase the surface area even more. Each gill is supported by a gill arch. 3. The gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion. 4. Blood flows through the gill plates 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 is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.
How are fish ventilated?
1. The fish opens its mouth, which lowers the floor of the buccal cavity (the space inside the mouth). The volume of the buccal cavity increases, decreasing the pressure inside the cavity. Water is then sucked into the cavity. 2. When the fish closes its mouth, the floor of the buccal cavity is raised again. The volume inside the cavity decreases, the pressure increases, and water is forced out of the cavity across the gill filaments. 3. Each gill is covered by a bony flap called the operculum (which protects the gill). The increase in pressure fores the operculum on each side of the head to open, allowing water to leave the gills.
How does one dissect fish gills?
1. Firstly, wear an apron or lab coat and gloves because the procedure is messy. 2. Place the fish in a dissection tray or on a cutting board. 3. Push back the operculum and use scissors to carefully remove the gills. Cut each gill arch through the bone at the top and bottom 4. Finish off by drawing the gill and labelling it.
Explain how ventilation works in insects.
1. Insects have microscopic air-filled pipes called trachae which they have for gas exchange. 2. Air moves into the trachae through pores on the insects surface called spiracles. 3. Oxygen travels down the concentration gradient towards the cells. Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere. 4. The trachae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells. The tracheoles also contain fluid, which oxygen dissolves in. 5. The oxygen then dissolves from this fluid into body cells. Carbon dioxide diffuses in the opposite direction. 6. Insects use rhythmic abdominal movements to change the volume of their bodies and move air in and out of the spiracles. When larger insects are flying, they use their wings to pump their thoraxes too.
How would one dissect the gaseous exchange system in an insect?
1. First, fix the insect to a dissecting board. You can put dissecting pins through its legs to hold it in place. 2. To examine the trachae, you'll need to carefully cut and remove a piece of exoskeleton (the insect's hard outer shell) from the along the length of the insect's abdomen. 3. Use a syringe to fill the abdomen with saline solution. You should be able to see a network of very thin, silvery-grey tubes - these are the trachae. They look silver because they're filled with air. 4. You can investigate the trachae under a light microscope using a wet mount slide. Again, the trachae will appear silver or grey. You should also be able to see rings of chitin in the walls of the trachae - these are there for support (like the rings of cartilage in a human trachea).