AQA Combined Science Biology Chapter Four

* The blood, the blood vessels and the heart make up the circulatory system. This transports substances to and from the body cells.

* Plasma has blood around the cells suspended in it and transported by proteins and other chemicals around the body.

* Your red blood cells contain haemoglobin that binds to oxygen to transport it from the lungs to the tissues.

* White blood cells help to protect the body against infection.

* Platelets are cell fragments that start the clotting process at wound sites 

* Blood flows around the body in the blood vessels. The main types of blood vessels are, arteries, veins and capilliares.

* Substances diffuse in and out of the blood in the capillaries.

* Valves prevent back flow, ensuring that blood flows in the right direction.

* Human beings have a double circulatory system.

* The heart is an organ that pumps blood around the body.

* Heart valves keep the blood flowing in the right direction.

* Stents can be used to keep narrowed or blocked arteries open.

*Statins reduce chlolesterol levels in the blood, reducing risk of coranary heart disease.

* Damaged heart valves can be replaced using biological or mechanical valves.

* The resting heart rate is controlled by a group of cells in the right atrium that form a natural pace maker.

* Artifical pacemakers are electrical devices used to correct irregularites in the heart rhythm.

* Artifical hearts are occasionally used to keep paitents alive while they wait for a transplant, or for their heart to rest as an aid to recovery.

* The lungs are in your chest cavity, protected by your ribcage, and seperated from your abdomen by the diaphgram.

* The alveoli provide a very large surface area and a rich supply of blood capilaries. This means gases can diffuse into and out of the blood as efficently as possible.

* Plant tissues are collections of cells specailised to carry out specific functions.

* The structure of the tissues in plant organs is related to their functions.

* The roots, stem, and leaves form a plant organ system for the transport of substances around the plant.

* Plants have separate transport systems.

* Xylem tissue transports water and mineral ions from the roots to the stems and leaves.

* Pholem tissue transprts dissolved sugars from the leaves to the rest of the plant, including the growing reigons and storage organs.

* The loss of water vapour from inside a plant from the surface of it's leaves is known as transpiration.

* Water is lost through the stomata, which open to let in carbon dioxide for photosynthesis.

* The stomata and gaurd cells control gas exchange and water loss. 

* Factors that increase the rate of photosynthesis or increas stomatal opening will increase the rate of transpiration. These factors include temprature, humidity,air flow, and light intesnity.

*Transpiration is more rapid in hot, dry, windy or bright conditions.