Organising animals and plants (The blood and blood vessels (The blood is a…
Organising animals and plants
The blood and blood vessels
The blood is a unique tissue based on a liquid called plasma Plasma carries red and white blood cells, and platelets suspended in it. It also carries dissolved substances around the body.
The red blood cells are the most prominent cell in the body and pick up oxygen from the lungs and carry it to the required cell. They have adaptations to help it complete this role, such as them being packed with haemoglobin that binds to oxygen. They have no nucleus, making more space for haemoglobin.
White blood cells are much larger than red, and there are fewer of them. Some white blood cells from antibodies against microorganism. Some form antitoxins against poisons, whilst other engulf invading bacteria and viruses, digesting them.
Platelets are small fragments of cells, with no nucleus, that help the blood clot at the site of a wound. The clot dries and hardens to form a scab, which protects the new skin as it grows and stops bacteria from entering the body through the wound.
Blood is carried around the body through three main types of blood vessel. The artery carries the blood away from the heat. The veins carry blood away from the organs and towards the heart. Arteries have much thicker walls than veins, as a cut artery is extremely dangerous. Finally, the capillaries form a huge network of tiny vessels that link the arteries and the veins.
The heart is an organ that pumps blood around the body. It is made of two pumps that beat together. The walls of the heart are almost entirely muscle.
The structure of the human heart is perfectly adapted for pumping blood to the lungs and body. Blood enters the top chambers of the heart, which are called the
. The blood coming into the right atrium from the
is deoxygenated blood from the body. The blood coming into the left atrium in the
is oxygenated blood from the lungs. The atria contract together and force blood down into the ventricles. Valves close to stop the blood flowing backwards out of the heart.
Problems associated with the heart
Coronary heart disease is a disease where the coronary arteries that supply blood to the heart muscle become narrow. If the blood flow is reduced, the supply of oxygen to the heart muscle is reduced. This can cause pain, a heart attack, and even death.
Doctors will solve coronary heart disease with a stent. A stent is a metal mesh that is placed in the artery. A tiny balloon is inflated to open up the blood vessel and the stent at the same time. The balloon is deflated and removed but the stent remains in place, holding the blood vessel open. The blood can then flow freely. Doctors can implant a stent with general anaesthetic.
Doctors can also prescribe statins to anyone at risk of cardiovascular disease. They reduce blood cholesterol levels and this slows down the rate at which fatty material is deposited in the coronary arteries.
Helping the heart
Over time, heart valves may become stiff and not open fully. This become dangerous as it makes the heart less efficient. Doctors can operate and replace faulty heart valves. Long lasting mechanical valves are made of materials such as titanium and polymers. An issue is that medication must be taken for life to prevent blood from clotting around it.
A group of cells in the right atrium of the heart act as a natural pacemaker, that sets a steady rhythm for the heart to beat at. If this fails or works incorrectly, an artificial pacemaker can be applied to help the heart beat regularly.
Whilst a pacemaker is usually enough to keep the heart beating steadily, sometimes it is not enough. Scientists have developed temporary hearts that can support the natural heart until it can be replaced. Artificial hearts can also be used to give a diseased heart a rest, so that it can recover. However, the resources needed to develop artificial hearts and the cost of each one means they are not yet widely used in patients.
Breathing and gaseous exchange
The lungs are found in the chest, and are separated from the digestive system by the diaphragm. The job of the ventilation system is to move air in and out of the lungs, which provides an efficient surface for gas exchange in the alveoli.
When you breathe in, oxygen rich air moves into the lungs. This maintains a steep concentration gradient with the blood. As a result, oxygen continually diffuses into the bloodstream through the gas exchange surface of the alveoli. Breathing out removes carbon dioxide from the lungs. This maintains a concentration gradient so carbon dioxide can continually diffuse out of the bloodstream into the air in the lungs.
The lungs are specially adapted to make gas exchange more efficient. They are made of clusters of alveoli that provide a large surface area. This is important for achieving the most effective diffusion of oxygen and carbon dioxide. Gas exchange takes place down the steepest concentration gradients possible. This makes the exchange rapid and effective.
Tissues and organs in plants
The specialised cells in multi cellular plants are organised into tissues and organs. Epidermal tissues cover the surface and protect them. These cells secrete a waxy substance that waterproofs the surface of the leaf. Palisade mesophyll tissue contains lots of chloroplast, which carry out photosynthesis. Spongy mesophyll tissue contains some chloroplasts but has big air spaces and a large surface area to make the diffusion of gases easier. Xylem and phloem are the transport tissues in plants. Xylem carry water and dissolve mineral ions from the roots up to the leaves and phloem carry dissolved food from the leaves areound the plant
Transport systems in plants
Plants make glucose by photosynthesis in the leaves. This glucose is needed all over the plant. This is the same for water and mineral ions when they move from the soil into the roots. They are needed for every cell of the plant, so use two transport systems to move the materials.
Phloem transports sugars made by photosynthesis, and xylem transport water.
This process is vital in keeping the entire plant healthy.
Evaporation and transpiration
All over leaf surfaces are small openings known as the stomata. They open when the plant needs to allow air into the leaves.
CO2 from the atmosphere diffuses into the air spaces and then into the cells down a concentration gradient. Simultaniously, oxygen produced by photosynthesis is removed from the leaf by diffusion into the surrounding air. This maintains a concentration gradient for oxygen to diffuse from the cells into the air spaces of the leaf. The size of the stomata and their opening and closing is controlled by the guard cells.
As this water evaporates from the surface of the leaves, more water is pulled up through the xylem to take its place. This movement of water molecules throuhg the xylem from the roots to the leaves is known as the transpiration stream. It is driven by the evaporation of water from the leaves. So, anything that affects the rate of evaporation will also affect the transpiration.