The Blood Vessels

The 3 types of Blood Vessels are: Arteries which carry blood away from the heart. Capillaries which are involved with the exchange of materials at the tissues

Arteries- heart pumps blood at high pressures so artery walls are strong and elastic. Walls are thick compared to the size of the lumen. They contain thick layers of muscle so that they are strong and have elastic fibres which allow then to spring back. Arteries branch out into arterioles. 

Capillaries- arteriols branch out into capillaries which are really tiny. They carry blood very close to every cell in the body to exchange substances with them. They have permeable walls so that things can diffuse in and out. They supply food and oxygen and take away waste like CO2. Their walls are only one cell thick; this increases the rate of diffusion by decreasing the distance over which it occurs. Capillaries branch out into venules 

Veins- Venules join up to form veins. Blood is at lower pressure in the veins so walls dont need to be as thick as arteries. They have a bigger lumen to help the blood flow despite the lower pressure. They have valves to help blood flow in right direction.

Cross Section Area of vessels affect blood flow: As the total cross-section area of blood vessels increases the mean velocity of blood flowing though vessels decreases ie blood flows slower through capillaries than in the veins and arteries. Although capilaries are tiny they have a huge total cross-section meaning blood flows slower through capillary beds allowing more time for substances to exchange. The mean pressure of blood is higher at the arteries as they're closer to the heart but the larger total cross-section area of capillaries causes the pressure to fall.

Transport System: Blood has plasma, platelets, red blood cells (rbc) and white blood cells (wbs)

Plasma:is the pale yellow liquid that transports everything around the body including- RBCs, WBCs, Platelets, Water, Digested food products like glucose and amino acidsfrom gut to body cells, Carbon Dioxide from body cells to lungs, Urea from liver to Kidneys, Hormones and Antibodies

RBCs: They transport oxygen from the lungs to the whole body. The structure of them are adapted to their function- small biconcave disc shape to give it a large surface to volume ratio for absorbing and releasing oxygen.have haemoglobin which gives it its colour and contains lots of ironand in the lungs it combines with oxygen to become oxyhaemoglobin.they dont have a nucleus to free up space for haemoglobin so they can carry more oxygen. They are small + flexible so they can pass through small capillaries 

Plants have 2 transport vessels- xylem and phloem. Both types of vessels go to every part of the plant but are totally different

Phloem- They are made in columns of living cells which are called seive tube cells. Seive tube cells dont have a nucleus meaning they can't survive on their own so each seive tube cell has a companion cell. Companion cells carry out the living functions for themselves and the seive cells. Phloem vessels transport food ie. sugars up and down the stem to growing and storing tissues. This movement is known as translocation. Food in the phloem can go both ways in any direction, up or down

Xylem- made of dead cells joined end to end with no end walls between them and a lumen in the middle. The thick side walls are made of cellulose. Theyre strong and stiff which gives the plant support. The plant is also strengthened by a material called lignin. They carry water from the root to the shoot in the transpiration stream. Water and minerals only go up the xylem. 

-It is caused by the evaporation and diffusion of water from a plants surface. Transpiration happens at the leaves

-Evaporation and Diffusion creates a shortage of water in the leaves so water is drwn up from the rest of the plant through xylem vessels to replace it. This means that more water is drawn up the roots so there is a constant transpiration stream of water through the plant. 

-Transpiration is a side effect of how leaves are adapted for photosynthesis therfore they have stomata so gases can be exchanged easily. There is more water inside the plant than there is out in the air so the water leaves through the plant through the stomata by diffusion.

-There are some benefits of transpiration inc: the stream of water from the ground helps to keep the plant cool, It provides the plant with a constant supply of water for photosynthesis, Water creates turgur pressure in plants which helps to support the plant and stop it from wilting, Minerals needed by pplants can be brought up from soil with the water.

What are the factors that effect the rate of transpiration?

Increase in light intensity- the brighter the light the greater the transpiration rate. Bright light increases rate of photosyntheis opening up the the stomata to allow CO2 to come in. Stomata starts to close when it starts to get dark so photosynthesis can't happen. When stomata is closed water cannot escape.Increase in Temperature-the warmer it is the faster the rate of transpiration. When warm water particles have more energy to evaporate and diffuse out of stomata.Increase in air Movement- if theres lots of air movementaround the leaf transpiration happens faster. If there is no air movement the water vapour surrounds the leaf and doesnt move. This means that there is a high concentration of water particles outiside leaf as well as inside. If it is windy then water vapour is swept away maintaining low concentration of water vapour outise in the air. Now diffusion can happen faster from a area of high conc. to one with lower conc.

Plant adaptations to reduce loss of water from leaves: Waxy Cutivle covering upper epedermis to make upper surface of leaf waterproof, Most stomata found near bottom of leave where it is darker and cooler to slow down the rate of diffusion, The bigger the stomata  and the more there are the more water is lost so plants in hot climates have smaller and fewer stomata and none on the upper epidermice as they need to conserve the water they have.

The function on Stomata:

-Close automatically when the supply of water starts to dry up.

-Guard cells have a special kidney shape which opens and closes stomata as guard cells go turgid or flacid. When guard cells are flaccid stomata closes when guard cells are turgid stomata opens.

-Thin outer walls and thin inner walls makes this opening and closing function possible.

-Open stomata allows gases in and out for photosynthesis

-Stomata are sensitive to light so open in the day and close during the night. This way they can conserve water for photosynthesis