-
We need your support!
We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
Click here to Donate Now (View Announcement)
Urgent Help In Biology!!!!
- Thread starter filza94
- Start date
- Messages
- 2,884
- Reaction score
- 415
- Points
- 93
We thank you!filza94 said:hmm jux thank my all posts datz wat i want...
- Messages
- 49
- Reaction score
- 0
- Points
- 0
filza94 said:
Lmao gladly, I'd rather go actually study than waste my time asking people to help me on the simplest topics
God help you in your paper
Just make it a point whenever you answer a Biology Theory question, look at the demand of the question, the amount of marks associated with that question and try to figure out what the examiner really wants you to stuff into your answer sheet. Jot down those points with a pencil on the side of the question before fairing them up. Then find good connectives that will link all these points together so that they co-relate. Trust me, the examiner gets impressed if you draft out your answer in a well structured way. I think 40% of Biology theory questions merely demand student's "way" of answering the questions; the rest is simply knowledge
- Messages
- 59
- Reaction score
- 3
- Points
- 18
Circulation in plants
There are two types of vessels in plants :-
Xylem -- These vessels take water and mineral ions from the roots to the stem and the leaves.
Phloem -- takes iorganic substances and sugars from the leaves to the parts of the leaves that require them eg. the flowers, fruits and roots.
Xylem travels only upwards, wheras phloem travels in both directions.
Movement in xylem vessels
The cells which make up a xylem vessel are dead. They are joined together by a sticky substance called lignin, these cells are therefore said to be "lignified". This causes the xylem vessels to be impermeable.
There are three mechanisms which contribute to the movement of water through the xylem vessel.
• Capillarity --- Xylem vessels are often very small in plants and therefore water is able to travel up them via capillary action. The water molecules stick to the side of the vessel and slowly "climbs up". However this mechanism does not account for the greater distance that water can travel in trees.
• Root pressure ---- Some plants can produce a water potential gradient by actively transporting mineral ions to the top of the plant. The water potential on the top of the plant is much greater than the bottom of the plant, therefore the water moves up to the top.
• Cohesion-tension --- As leaves transpire, water evaporates to the dry surroundings outside the plant. Water molecules stick to each other by hyrdogen bonds. This is known as cohesion. So as they leaves transpire the water molecules are all pulled up the plant. Water molecules also stick to the sides of the vessel which helps to speed this mechanism up. This is known as adhesion.
Movement through cells
The Apoplastic pathway --- The water and mineral ions moves through the cells walls and through the spaces between the cells.
The symplatic pathway --- The contents of neighbouring cells are joined by thin strands of cytoplasm, known as plasmodemata. Water and other substances can move from one cell to the next via these structures. This is very useful because the substances do not have to cross cell membranes.
There are two types of vessels in plants :-
Xylem -- These vessels take water and mineral ions from the roots to the stem and the leaves.
Phloem -- takes iorganic substances and sugars from the leaves to the parts of the leaves that require them eg. the flowers, fruits and roots.
Xylem travels only upwards, wheras phloem travels in both directions.
Movement in xylem vessels
The cells which make up a xylem vessel are dead. They are joined together by a sticky substance called lignin, these cells are therefore said to be "lignified". This causes the xylem vessels to be impermeable.
There are three mechanisms which contribute to the movement of water through the xylem vessel.
• Capillarity --- Xylem vessels are often very small in plants and therefore water is able to travel up them via capillary action. The water molecules stick to the side of the vessel and slowly "climbs up". However this mechanism does not account for the greater distance that water can travel in trees.
• Root pressure ---- Some plants can produce a water potential gradient by actively transporting mineral ions to the top of the plant. The water potential on the top of the plant is much greater than the bottom of the plant, therefore the water moves up to the top.
• Cohesion-tension --- As leaves transpire, water evaporates to the dry surroundings outside the plant. Water molecules stick to each other by hyrdogen bonds. This is known as cohesion. So as they leaves transpire the water molecules are all pulled up the plant. Water molecules also stick to the sides of the vessel which helps to speed this mechanism up. This is known as adhesion.
Movement through cells
The Apoplastic pathway --- The water and mineral ions moves through the cells walls and through the spaces between the cells.
The symplatic pathway --- The contents of neighbouring cells are joined by thin strands of cytoplasm, known as plasmodemata. Water and other substances can move from one cell to the next via these structures. This is very useful because the substances do not have to cross cell membranes.
- Messages
- 59
- Reaction score
- 3
- Points
- 18
sry.. didnt make!
i will repost!
i will repost!
- Messages
- 59
- Reaction score
- 3
- Points
- 18
Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants (similar to sweating), especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants they are more numerous on the undersides of the foliage. The stoma are bordered by guard cells that open and close the pore. Leaf transpiration occurs through stomata, and can be thought of as a necessary "cost" associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients and water from roots to shoots.
Mass flow of liquid water from the roots to the leaves is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem.
The rate of transpiration is directly related to the evaporation of water molecules from plant surface, especially from the surface openings, or stoma, on leaves. Stomatal transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the cuticle of the leaves and young stems. The amount of water given off depends somewhat upon how much water the roots of the plant have absorbed. It also depends upon such environmental conditions as light intensity, humidity, winds and temperature. A plant should not be transplanted in full sunshine because it may lose too much water and wilt before the damaged roots can supply enough water. Transpiration occurs as the sun warms the water inside the blade. The warming changes much of the water into water vapour. This gas can then escape through the stomata. Transpiration helps cool the inside of the leaf because the escaping vapor has absorbed heat, the degree of stomatal opening, and the evaporative demand of the atmosphere surrounding the leaf. The amount of water lost by a plant depends on its size, along with surrounding light intensity,temperature, humidity, and wind speed (all of which influence evaporative demand). Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate.
A fully grown tree may lose several hundred gallons of water through its leaves on a hot, dry day. About 90% of the water that enters a plant's roots is used for this process. The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced; the transpiration ratio of crops tends to fall between 200 and 1000 (i.e., crop plants transpire 200 to 1000 kg of water for every kg of dry matter produced).
Transpiration rate of plants can be measured by a number of techniques, including potometers, lysimeters, porometers, photosynthesis systems and heat balance sap flow gauges.
Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced leaf areas, sunken stomata and hairs to reduce transpiration and conserve water. Many cacti conduct photosynthesis in succulent stems, rather than leaves, so the surface area of the shoot is very low. Many desert plants have a special type of photosynthesis, termed crassulacean acid metabolism or CAM photosynthesis in which the stomata are closed during the day and open at night when transpiration will be lower.
Mass flow of liquid water from the roots to the leaves is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem.
The rate of transpiration is directly related to the evaporation of water molecules from plant surface, especially from the surface openings, or stoma, on leaves. Stomatal transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the cuticle of the leaves and young stems. The amount of water given off depends somewhat upon how much water the roots of the plant have absorbed. It also depends upon such environmental conditions as light intensity, humidity, winds and temperature. A plant should not be transplanted in full sunshine because it may lose too much water and wilt before the damaged roots can supply enough water. Transpiration occurs as the sun warms the water inside the blade. The warming changes much of the water into water vapour. This gas can then escape through the stomata. Transpiration helps cool the inside of the leaf because the escaping vapor has absorbed heat, the degree of stomatal opening, and the evaporative demand of the atmosphere surrounding the leaf. The amount of water lost by a plant depends on its size, along with surrounding light intensity,temperature, humidity, and wind speed (all of which influence evaporative demand). Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate.
A fully grown tree may lose several hundred gallons of water through its leaves on a hot, dry day. About 90% of the water that enters a plant's roots is used for this process. The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced; the transpiration ratio of crops tends to fall between 200 and 1000 (i.e., crop plants transpire 200 to 1000 kg of water for every kg of dry matter produced).
Transpiration rate of plants can be measured by a number of techniques, including potometers, lysimeters, porometers, photosynthesis systems and heat balance sap flow gauges.
Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced leaf areas, sunken stomata and hairs to reduce transpiration and conserve water. Many cacti conduct photosynthesis in succulent stems, rather than leaves, so the surface area of the shoot is very low. Many desert plants have a special type of photosynthesis, termed crassulacean acid metabolism or CAM photosynthesis in which the stomata are closed during the day and open at night when transpiration will be lower.