Biology - Plants and photosynthesis

When do plants respire or photosynthesis?

Plants respire during the day and night. They only photosynthesis during the day when there is sunlight. The net (overall) effect depends on the time of day and the light intensity. Photosynthesis doesn't occur at night. When there is no photosynthesis, there is a net release of carbon dioxide and a net uptake of oxygen. If there is enough light during the day, then: the rate of photosynthesis is higher than the rate of respiration there is a net release of oxygen and a net uptake of carbon dioxide

What is the experiement that investigates the transpiration rate?

A potometer is used to estimate transpiration rates. It measures the water intake by a plant, which is related to the water loss by the leaves. How the experiment works: Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to increase the surface area available for water uptake. Assemble the potometer in water and insert the shoot underwater, so no air can enter. Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water. Check the apparatus is watertight and airtight. Dry the leaves, allow time for the shoot to adjust and shut the tap. Remove the end of the capillary tube from the beaker of water until one air bubble has formed, then but the end of the tube back into the water. Record the starting position of the air bubble. Start a stopwatch and record the distance moved by the bubble per unit time. Keep conditions conditions constant throughout the experiment, e.g. the temperature and air humidity.

How do you test for starch to investigate photosynthesis?

Boil some water using a Bunsen burner Hold the leaf in forceps and plunge it into the boiling water for 5 seconds. This will kill the cells, stop all chemical reactions and make the leaf permeable to alcohol and iodine solution later on. Put the leaf at the bottom of a test-tube and cover it with ethanol. Place the test-tube in the hot water and leave it for 5 minutes. The alcohol will boil and dissolve out the chlorophyll in the leaf. Your leaf should be white or very pale green. Fill the test-tube with cold water and the leaf will should float to the top. Use forceps to spread the leaf flat in a petri dish. Use a dropping pipette cover the leaf with iodine solution for one minute. Take the leaf to the sink and holding it on the petri dish, wash away the iodine solution with some cold water. If the leaf is blue-black starch is present.

How does the concentration of carbon dioxide affect the rate of photosynthesis?

Carbon dioxide is one of the reactants in photosynthesis. If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase. At some point, a factor may become limiting.

What do nitrates do and what is the deficiency if plants don't get enough of it?

Contain nitrogen for making amino acids and proteins. These are needed for cell growth. If a plant can't get enough nitrates it will be stunted and older leaves will turn yellow.

What do phosphates do and what is the deficiency if plants don't get enough of it?

Contain phosphorus for making DNA and cell membranes. Needed for respiration and growth. Plants without enough phosphate have poor root growth and their older leaves turn purple.

What is diffusion?

Diffusion is when particles move from an area of high concentration to an area of low concentration.

What is the experiment that shows light is needed for photosynthesis?

Get a plant that's been grown without any light. E.g. in a cupboard for 48 hours. This means that it has used up its starch stores. Cut a leaf from the plant and test it for starch using iodine solution. The leaf won't turn blue-black showing that light is needed for photosynthesis.

Where does photosynthesis happen?

Happens in leaves of all green plants. Happens inside chloroplasts, which are mostly found in leaf cells. Chloroplats contain a pigment called chlorophyll, which absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose and oxygen.

What is photosynthesis?

It is a chemical reaction that takes place inside a plant, producing food (glucose) for the plant to survive. Carbon dioxide, water and light are all needed for photosynthesis to take place. Photosynthesis converts light energy into chemical energy, which is stored in the glucose. This chemical energy is released when glucose is broken down during respiration.

How are leaves adapted for gas exchange?

Leaves are broad - large surface area for diffusion. Thin - gases only have to travel a short distance to reach the cells where they're needed. Air spaces inside the leaf - lets gases like carbon dioxide and oxygen move easily between cells. Also increases the surface area for gas exchange. Lots of stomata on lower surface - let gases diffuse in and out.

What is the structure of a leaf and how is each adapted for photosynthesis?

Leaves are broad, so there's a large surface area exposed to light. Epidermis is thin and transparent - to allow more light to reach the palisade cells. Thin cuticle made of wax - to protect the leaf from infection and prevent water loss without blocking out light. Palisade cell layer at top of leaf - to absorb more light and increase the rate of photosynthesis. Spongy layer - air spaces allow carbon dioxide to diffuse through the leaf. Palisade cells contain many chloroplasts - Therefore they are near to the top so they can absorb all the available light.

What factors affect the rate of photosynthesis?

Light intensity Carbon dioxide concentration Temperature

What factors affect transpiration?

Light intensity Temperature Wind speed Humidity

What are the four main mineral ions plants need for growth?

Nitrates Phosphates Potassium Magnesium Plants need this elements so they can produce important compounds. They get these elements from mineral ions in the soil. If there aren't enough of these mineral ions in the soil, plants suffer deficiency symptoms.

What does phloem transport?

Phloem tubes transport food. The phloem transports sugars, like sucrose, and amino acids from where they're made in the leaves to the other parts of the plant. This movement of food substances around the plant is known as translocation.

What are the waste products of metabolism and photosynthesis?

Plants Plants need to excrete excess carbon dioxide and oxygen. Carbon dioxide is a waste product of aerobic respiration in plant cells. Oxygen is a waste product of photosynthesis. The leaf Unlike animals, plants do not have specialised excretory organs. Excess carbon dioxide and oxygen are excreted from the plant through the stomata in the leaves.

How does the stomata work?

Plants obtain the gases they need through their leaves. They require oxygen for respiration and carbon dioxide for photosynthesis. The stomata control gas exchange in the leaf. Each stomata can be opened or closed, depending on how turgid its guard cells are. In the light, the guard cells absorb water by osmosis, become turgid and the stoma opens. In the dark, the guard cells lose water, become flaccid and the stoma closes. When water flows into the guard cells by osmosis, their turgidness increases and they expand. This causes the guard cells to bend and draw away from each other, so the pore opens. If the guard cells loose water the opposite happens and the pore closes.

What is the experiment to investigate the effect of light intensity of the production of oxygen (the rate of photosynthasis)?

Pond-weed can be used to measure the effect of light intensity on the rate of photosynthesis. The faster the rate of oxygen production, the faster the rate of photosynthesis. How the experiment works: The gas syringe should be empty to start with. Sodium hydrogen-carbonate may be added to the water to make sure the plant has enough carbon dioxide. A source of white light is placed at a specific distance from the pond-weed. The pond-weed is left to photosynthesise for a set amount of time. As it photosynthesises, the oxygen released will collect in the empty capillary tube. At the end of the experiment, the syringe is used to draw the gas bubble in the tube alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of oxygen produced. The experiment is repeated again with the light source placed at different distances from the pond-weed. The control variables are things like temperature, amount of time the pond-weed has been left to photosynthesis and the amount of carbon dioxide. The apparatus can be altered to measure the effect of temperature of carbon dioxide.

What does magnesium do and what is the deficiency if plants don't get enough of it?

Required for making chlorophyll - needed for photosynthesis. Plants without enough magnesium have yellow leaves

What is a limiting factor?

Something which stops photosynthesis from happening any faster. The limiting factor depends of the environmental conditions. E.g. In winder - temperature low At night - no sunlight

How does light intensity affect transpiration?

The brighter the light, the greater the transpiration. Stomata begin to close as it gets darker. Photosynthesis can't happen in the dark, so they don't need to open to let CO2 in. When the stomata are closed, very little water can escape.

How does humidity affect transpiration?

The drier the air around the leaf, the faster transpiration happens. This is like what happens with air movement. If the air is humid there's a lot of water in it already, so there's not much of a difference between the inside and outside of the leaf. Therefore diffusion doesn't happen because the particles earn't moving from a high concentration to a low concentration - because they are both high concentration.

How does wind speed affect transpiration?

The higher the wind speed around a leaf, the greater the transpiration rate. If wind speed around a leaf is low, the water vapour just surrounds the leaf and doesn't move away. This means there's a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn't happen as quickly. If it is windy, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly, from an area of high concentration to an area of low concentration.

What is the experiment that shows that carbon dioxide is needed for photosynthesis?

The soda lime will absorb carbon dioxide out of the air in the jar. If you leave the plant in the jar for a while and then test a leaf for starch, it wont turn blue-black. Thus shows that no starch has been made in the leaf, which means that carbon dioxide is needed for photosynthesis.

How does temperature affect transpiration?

The warmer it is, the faster transpiration happens. When it's warm the water particles have more energy to evaporate and diffuse out of the stomata.

What does potassium do and what is the deficiency if plants don't get enough of it?

To help the enzymes needed for photosynthesis and respiration. If there's not enough potassium in the soil, plants have poor flower and fruit growth and discoloured leaves.

What is transpiration?

Transpiration is caused by the evaporation and diffusion of water from a plant's surface. Most transpiration happens at the leaves. This evaporation creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels. This means more water is drawn up from the roots, and so there's a constant transpiration stream of water through the plant. Transpiration is a side effect of photosynthesis. When gases diffuse in and out of the stomata water also escapes because there's more water inside the plant than in the air outside.

What does the starch test show?

Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue-black with iodine solution. This shows the importance of chlorophyll in photosynthesis. Also if a plant can't photosynthesis then it can't make starch.

How does light intensity affect the rate of photosynthesis?

Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide and a suitable temperature. Increasing the light intensity increases the rate of photosynthesis , until some other factor - a limiting factor - becomes in short supply so then the rate of photosynthesis is constant.

What are the two main types of transport systems plant have?

Xylem and phloem

What does xylem transport?

Xylem tubes transport water and minerals. The xylem carry water and mineral salts from the roots up to the shoot to the leaves in the transpiration stream.

What is the balanced word and symbol equation of photosynthesis?

Symbol equation: 6CO2 + 6H2O ->(sunlight) C6H12O6 + 6O2 Word equation: Carbon dioxide + water ->(sunlight) glucose + oxygen

How does the temperature affect the rate of photosynthesis?

The chemical reactions that combine carbon dioxide and water to produce glucose are controlled by enzymes. Therefore the rate of reaction will be affected by temperature. At low temperatures, the rate of photosynthesis is low because fewer molecular collisions occur per unit time between enzymes and substrates. As you increase the temperature the number of molecular collisions increase per unit time . At high temperatures, enzymes are denatured.

What is the word and symbol equation for aerobic respiration in plants?

Word equation: Glucose + oxygen -> carbon dioxide + water Symbol equation: C6H12O6 + 6O2 → 6CO2 + 6H2O