B3

?

Gas exchange in plants

Surface of the plant cell covered in epidermal cells. Under these densely packed palisade mesophyll. Under that is losely packed cells called spongy mesophyll. At the bottom of the leaf more epidermal cells.These have tiny pores called stomata. Job of epidermal cells is to protect the plant. The palisade mesophyll is the main site of photosynthesis. These are packed with that contain chlorophyll. Spongy mesophyll allows diffusion of gas in the leaf and this is because cells loosely packed and lots of air spaces between them. Stomata's pores allow gases to move in and out of the leaf. CO2 diffuses into leaf through stomata, diffuses through spongy mesophyll up to the palisade cells use photosynthesis. Because palisade cells use CO2 have concentration gradient. Higher concentration gradient at bottom of leaf than neat palisade cells. Because leaf thin, difusion short short distance and high concentration gradient c02 diffuses quick. Oxygen produced from palisade cells so diffuses back through spongy mesophyll etc. 

Plants respire all the time, only photosynthesis in light. Night, take in c02 release 02, respiring. Plants can lose water vapour from: hot weather, windy and dry. If can't replace water quick enough, water closed to reduce more water leaving. Size stoamta controlled by 2 guard cells. guard cells can change their shape. 

1 of 11

Transport systems in plants

Water enters roots of plants by osmosis. Root hair cells are adapted to ensure that lots of water is absorbed. Root hair cells have a large surface area and use active transport to move ions into the cell. This makes the inside of the cell more concentrated that the soil so more water enters by osmosis. 

Water now passes into ylem vessels and makes it way up the leaves. The water then moves by osmosis to palisade cells where used in photosynthesis. A lot of water also evaporates.

Movement of water from roots through xylema and out of leaves called transpiration stream. 

Gloucose from photosynrhesis is converted to sugars and is passed on in the phloem. Phloem vessels run up and down the whole plant. The sugar is then transported from the phloem to:  storage organs or growing regions. 

2 of 11

The kidneys

Homeostasis- Keeping the internal conditions in the body e.g. concentration glucose, ions, water and waste products

2 main ways products made in the body; carbon dioxide produced by aerobic respiration removed by lungs during breathing. Urea is produced in liver by breakdown of amino acids, remove from bloodstream by the kidneys and leaves the body in urine. 

Water and ions such as Na+ enter the body when eat and drink. If water level and ions not controlled, water can move in and out of cells by osmosis and damage them. 

Humans have 2 kidneys, blood enters kidney through artery and this blood contains waste product urea. The kidey removes this urea which pases out as urine and stored in bladder. Urea also contains water and ions.  Blood leaves kidney through a vein and you can see blood now contains no urea. 

How the kidneys remove molecules from the blood: First blood passes capillaries where small moleules are filtered out of blood including urea glucose ions and water, these pass through a tube. All of the glucose and some of the ions and some water is reabsorbed back into the blood.Urea,excess ion + excess water is released as urine.The kidneys carry out homeostasis.

3 of 11

Treating kidney disease

Treatment:n Kidney dialysis: several hours, few times a week. Usually in hospital. The patient blood passes over a semi-permeable membrane. Allows small moclecules such as urea and water through. It wont allow large molecules such as proteins to pass through. Blood cells also too large for membrane. On the other side of the membrane dialysis fluid. This contains useful substances e.g. glucose in same concentration as found in blood. Dialysis also contains no urea. We've got a concentrartion gradient for urea. Urea diffuses from blood into dialysis fluid. Dialysis fluid contstantly refreshed ensure always large concentration gradient for urea. Concentration of useful substances such as water, glucose and ions is the same in the dialysis fluid as in the blood. There is no net diffusion of these substasnces. This is very inconcieinient however as need to keep on aregular diet and take a long time. 

Kidney transplant: The diseased kidney is replaced with a healthy kidney from a donor. However sometimes this may be rejected The cells of the donated kidney are convered in molecules that the patient body sees as foreign, antigens. These can be attacked by antibodies in patients blood. If this happens kidney rejected. 

2 ways prevent rejection: try to find kidney with closely matched tissue type; treat patient with drugs to weaken the immune system. 

4 of 11

DiIalysis v Kidney Transplant

Dialysis:

No shortage of dialysis machines

Requires strict diet and frequent treatments to reduce urea production and salt intake

Expensive long term

Kidney transplant:

Shortage of kidney donors

Allows patient to lead normal life

Only expensive initially. 

5 of 11

Control of body temperature

Body temperature controlled by brain-thermoregulatory centre in brain, this monitors temp blood passing.

Temp receptors in skin- monitor temperature in skin. These send electrical impulses to the brain's thermoregulatoru impulses to the brain's thermoregulatory centre giving it info about skins temp.

Body temp too high- sweat glands release sweat onto surface of skin. Sweat evaporates, takes energy from body and cools body down. On a hot day body conserves water by producing less urine. Also need to replace lost water by drinking more fluid. Also by flushing- blood vessels supplying skin capilaries dialate. More blood flows through capilaries and more heat lost. 

Body temp too low- Blood vessels supplying skin capillaries constrict. Less blood flows through capillaries and less heat is lost. When we shiver, out muscles contract, to generate the energy for this, the muscles increase rate of respiration. Also releases heat which warms the body. 

6 of 11

Control of blood glucose

Glucose used by cells in respiration to release enrgy. Most glucose in diet comes from starch. Excess glucose is stored as glycogen in muscles and the liver. 

After a meal, blood glucose levels rise. The pancreas detects the rise and releases the hormone insluin. Insulin causes cells to take up more glucose. Glucose is also stored as gylcogen.Blood glucsoe return back to normal levels. Between meals, blood glucose levels fall. The pancreas detects this fall and releases the hormone glucogen. Glycogen converted back to glucose to bre realeased back into blood. Blood glucose levels return back to normal. 

Type 1 diabetes: Pancreas does not produce enough insulin. Blood glucose can rise to a high level espec. after a meal. We can treat this with insulin injections, diet and exercise.  

7 of 11

Deforestation

Why is it happening?

-Timber- mahogany/teak, make furniture     -Grazing cattle- provide beef to food industy

-Rainforests- cleared to make space to provide land to grow crops. Many crops ethanol biofuels

Negative effects:

-Loss of biodiversity, animals and plants. As ot os redicomg planets biodiversity.  We could be losing species that could provide useful medicines.

-Carbon Dioxide- Deforestation increases it in atmosphere. Burning trees and decomposition by microorganisms releases corabon dioxide.

-Cutting down trees also reduces acmount carbon dioxide taken up by photosynthesis and trapped in wood. 

-Methane ghg.Land taken grazing cattle+cows release lots methane. Rice grown warm waterlogged conditions- ideal decomposers. Produce methane released into atmoshpere. 

8 of 11

Peat Bogs

1. Peat bogs areas land acidic and waterlogged. Plants that live bogs don't fully decay when die bc not enough oxygen. Partly-rotted plants gradually build up to form peat.

2. Carbon in plants often stored in the peat instead of being released into the atmosphere.

3. However, peat bogss often drained so that area can be used as farmland or peat cut up and dried to use as fuel. Peat often sold as compost. 

4. Peat stars to decompose when bogs drained, so carbon dioxide released. If continue destroy peat bogs, more carbon dioxide released, bigger green house effect.

5. One way stop thisbuying peat free compost for gardens and reduce the demand for it. 

9 of 11

Global warming and biogas

Carbon dioxide increase due to burning fossil fuesls and coal and deforestation. Methane increases from, catlle and rice field. 

An increase in earth temp for a few degrees lead to: changes in earths climate eg. rainfall pattern. Rising sea levels and reduced biodiversity and changes in species distribution and migration patterns eg. birds. 

Carbon dioxide in waters lakes and ponds dissolve. Crops such as sugar can be converted to ethanol through fermentation by yeast. Ethanol can be blended with petrol to make biofules for cars. Biofuels redces amount CO2 released. As plants took in the gas photosynthesis. 

Bioga\s formed when bacteroa carry out anearobic fermentation on carbohydrates such as leftover food, manure eod cows. Biogas mainly methane. We often find biogas extractors on landfull sites. That's beneficial as the methane produces would otherwise escape into the atmosphere. Methane is a power greenhouse gas. Biogas electricity or heating or cooking. 

10 of 11

Small/ large scale biogas generation

  • Provide cooking fuel for famlies which may not be near fuel source. 
  • Can be sited right next to a source of fuel eg cowshed
  • Temp must be warm. If temp too cool bacteria respire slowly and biogas generation slows.  Too hot will denature enzymes in the bacteria. Can be placed underground to keep cool in hot countries. 
  • The biogas generator has to be cleaned out and refilled regularly which reduces production. (bath process)
  • Large amount biogas
  • Optimum temp controlled electronically, maximise production biogas.
  • Biogas generator can run continuosly generating more biogas.
  • Source of fuel may have to be transported to the biogas generator eg by lorry. If this burns fossil duels, then this will add to the carbon dioxide in the atmoshphere
11 of 11

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Nervous system, hormones and behaviour resources »