Section 7: Exchange And Transport Flashcards
What is a specialist exchange surface?
And 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. Single celled organisms exchange substances differently to multicellular organisms.
How do single called organisms exchange surfaces?
In single celled organisms, substances can diffuse directly into (or out of) the cell across the self-surface membrane. The diffusion rate is quick because of the short distances the substance have to travel and make a single celled organisms have a relatively high surface area to volume ratio.
How do multicellular organisms exchange surfaces?
In multicellular organisms, if you can across as my brain is too slow, the three reasons:
- some cells are deep within the body – there is a big distance between them and outside environment.
- Larger animals have a low surface area to volume ratio – it’s difficult to exchange enough substances to a supply a large volume of animals through a relatively small outer surface. 3.Multicellular organisms have a higher metabolic rate than single celled organisms so they use oxygen and glucose faster. So rather than using straightforward diffusion to absorb and excrete substances, multicellular organisms need specialised exchange surfaces (like the alveoli in the lungs).
How do exchange surfaces have special features to improve their efficiency and give examples.
They have a large surface area. Most exchange surfaces have a large surface area to increase their efficiency.
For example, the cells and plant roots grow into longhairs which stick out into the soil. Each branch of a root will be covered in millions of these microscopic hairs. This gives the root a larger surface area, which helps increase the rate of absorption of water (by osmosis) and mineral irons (by active transport) from the soil.
They are thin. Exchange surfaces are usually thin to decrease the distance of the substances being exchanged have to travel over, and so improve efficiency . Some are only one cell thick.
For example the alveoli are the gas exchange surface in the lungs. Each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium. Oxygen diffuses out of the alveolar space into the blood. Carbon dioxide diffuses in the opposite direction. The thin alveolar epithelium helps to decrease the distance over which oxygen and carbon dioxide diffusion takes place, which increases the rate of diffusion.
They have a good blood supply and/or ventilation. Another key feature of exchange surfaces is that they have a good blood supply and all are well ventilated to increase efficiency.
For example 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 (you breathe in and out) so the air in each alveolus is constantly replaced.
Also the gills are the gas exchange surface in fish. In the 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 very well ventilated – freshwater 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 is gas exchange?
In mammals, the lungs are gas exchange organs. They help to get oxygen into the blood (for respiration) and to get rid of carbon dioxide (made by respiring cells) from the body.
What is the structure of the gaseous exchange system?
As you breathe in, air enters the trachea (windpipe). The trachea splits into two bronchi– one bronchus leading to each lung. Each bronchus then branches off into smaller tubes called bronchioles. The bronchioles end in small air sacs called alveoli. This is where gases are exchanged. There are lots of alveoli in the lungs to provide a large surface area for diffusion. The rip cage, intercostal muscles and diaphragm all work together to move air in and out.
What are the key features of the gaseous exchange system?
The gaseous exchange system is made up of different cells and tissues. These help it to exchange gases efficiently.
Goblet cells (lining the airways) secrete mucus. The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.
The cilia are hair like structures in the surface of epithelial cells lining airways. They beat the mucus secreted by the goblet cells. This moves the mucus (plus the microorganisms and dust) upwards away from the alveoli towards the throat, where it’s swallowed. This helps prevent lung infections.
Elastic fibres in the walls of the trachea, bronchi, bronchioles and alveoli help the process of breathing out. On breathing in the lungs in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push the air out when exhaling.
Smooth muscle in the walls of the trachea, bronchi and bronchioles (except the smallest bronchioles) allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means there’s less resistance to airflow and air can move in and out of the lungs more easily.
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 distribution of features in the gaseous exchange system.
The trachea have large C-shaped cartilage, has smooth muscle, has elastic fibres, has goblet cells and has ciliated epithelium.
The Bronchi has smaller pieces of cartilage, smooth-muscle, elastic fibres, goblet cells, and ciliated epithelium.
A larger bronchiole has no cartilage, has smooth-muscle, has elastic fibres, has goblet cells and has ciliated epithelial.
A smaller bronchiole has no cartilage, has smooth-muscle, has elastic fibres, has no goblet cells and has ciliated epithelium.
The smallest bronchioles have no cartilage, has no smooth-muscle, has elastic fibres, has no goblet cells, and has no cilia.
The alveoli have no cartilage, has no smooth-muscle, has elastic fibres, has no goblet cells and has no cilia
What is ventilation?
Ventilation consists of inspiration (breathing in) and expiration(breathing out). It’s controlled by the movement of the diaphragm, intercostal muscles and ribcage.
Describe the steps of inspiration.
External intercostal and diaphragm muscles contract. 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). As the volume of the thorax increases lung pressure decreases (to below atmospheric pressure). This causes air to flow into the lungs. Inspiration is an active process – it requires energy.
Describe the steps of expiration.
The external intercostal and diaphragm muscles relax. The rip cage moves downwards and inwards and the diaphragm becomes curved again. The thorax volume decreases, causing the air pressure to increase (two above atmospheric pressure). Air is forced out of the lungs. Normal expiration is a passive process – it doesn’t require energy. Expiration can be forced though (e.g. if you want to blow out the candles on your birthday cake). During forced expiration, the internal intercostal muscles contract, to pull the ribcage down and in.
Describe the structure of gills.
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 or primary lamellae which gives a big service area for exchange of gases (and so increase the rate of diffusion). The gill filaments are covered in lots of tiny structures called gill plates or secondary lamella, which increases surface area even more. Each gill is supported by a gill arch. The gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion between the water and the blood.
Describe the counter current system.
In the gills of a fish, blood flows through the gill plates in one direction and water flows over in opposite direction. This is called a counter-current system. The counter-current system means that the water with a relatively high oxygen concentration always flows next to the
blood with a lower concentration of oxygen. This in turn means that the steep concentration gradient is maintained between the water and the blood – so as much oxygen as possible diffuses from the water into the blood.
How are fish gills ventilated in bony fish?
First, the fish opened 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. When this 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. Each gill is covered by a bony flap called that the operculum (which protects the gill). The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills.
Describe gas exchange and ventilation in insects.
Terrestrial insects have microscopic air-filled pipes called tracheae which they use for gas exchange. Air moves into the tracheae through pores on the surface called spiracles. Oxygen travels down the concentration gradient towards the cells. Carbon dioxide from the cells move down its own concentration gradient towards the spiracles to be released into the atmosphere. The tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells. The tracheoles also contains fluid, which oxygen dissolves in. The oxygen then diffuses from this fluid into body cells. Carbon dioxide diffuses in opposite direction.
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 wing movements to pump their thoraxes too.
