Bioenergetics Flashcards
(42 cards)
What is Photosynthesis
-Plants use light as their source of energy. To trap the light, plants carry out the process of photosynthesis.
-Because this takes in light energy, it is an endothermic reaction.
-Photosynthesis takes place in the leaves of the plant. These contain chlorophyll which can absorb light energy.
What is the Equation for Photosynthesis
Carbon Dioxide + Water 🡢 Glucose + Oxygen
Explain what is Meant by the Term Limiting Factor
A limiting factor is any factor which limits the rate of photosynthesis.
Describe what Happens to the rate of Photosynthesis as Light Intensity Increases
-As light intensity increases, the rate of photosynthesis increases steadily but only up to a certain point.
-Beyond that, it won’t make any difference- as light intensity increases, the rate will no longer increase.
-This is because it’ll either be carbon dioxide levels or temperature which is now the limiting factor, not light.
Describe how Greenhouses can Prevent Light from Becoming the Limiting Factor
-Use greenhouses constructed from glass or alternative materials that enable maximum transmission of light.
-Position plants for maximum light absorption.
Artificial lighting systems can be used:
-with increased light intensities
-that provide optimum wavelengths of light for photosynthesis
-that lengthen a plant’s growing season so that crops can be grown in more months of the year
Describe what Happens to the rate of Photosynthesis as Carbon Dioxide Levels Increases
-As carbon dioxide levels increase, the rate of photosynthesis increases steadily but only up to a certain point.
-Beyond that, it won’t make any difference- as carbon dioxide levels increase, the rate will no longer increase.
-This is because it’ll either be light intensity or temperature which is now the limiting factor, not carbon dioxide levels.
Describe how Greenhouses can Prevent Carbon Dioxide from Becoming the Limiting Factor
-Use paraffin heaters on a small scale
-On a larger scale, use carbon dioxide wastes from industrial processes that has been cleaned up before use
-Can use liquid carbon dioxide, applied through pipes, though this can be expensive
-Sometimes use fungi, grown as a mycelium in bags around the greenhouse, that add carbon dioxide through their respiration
Describe how Temperature Affects the Rate of Photosynthesis
-Often, if temperature is the limiting reactant, it is because it is too low. The enzymes needed for photosynthesis work more slowly at low temperatures.
-However, if the plant gets too hot, the enzymes needed for photosynthesis will become denatured.
Describe how Greenhouses can Prevent Temperature from Becoming the Limiting Factor
-Greenhouses help to trap the sun’s heat, and make sure that the temperature doesn’t become limiting.
-In winter, a farmer might use a heater as well to keep the temperature at the ideal level.
-In summer, it might get too hot so shades or a ventilation system might be installed to cool things down.
Describe the Benefit of Using Oil Burners in Greenhouses
-Burning oil generates heat and also releases carbon dioxide.
-Both temperature and carbon dioxide concentration can be limiting factors so by using oil burners, we ensure that the rate of photosynthesis is very high.
-Light intensity can also be a limiting factor but in practise, during the day, the light intensity in a greenhouse is very high.
Describe how Chlorophyll Levels Affect the Rate of Photosynthesis
-Variegated plants have a lower level of chlorophyll than non-variegated plants.
-This means that variegated plants can trap less light energy and will have a lower rate of photosynthesis.
Describe how Glucose is Used in Respiration
-Glucose produced by photosynthesis can be used for respiration.
-Glucose is broken down with oxygen to provide energy to the cells. Energy is released in a chemical reaction which takes place in the mitochondria.
-Carbon dioxide and water are the waste products.
What does it Mean that Burning Oil in Greenhouses has Economic Benefits
-Burning oil is expensive so this adds to a gardener’s costs.
-However, burning oil should increase the yield of crops.
-If the increased yield offsets the increased cost, then the gardener will make money. This is an economic argument.
Describe how Glucose is Used for Cellulose
-Energy transferred in respiration may be used to build smaller molecules into bigger molecules.
-Glucose is converted into complex carbohydrates such as cellulose which is used to strengthen cell walls.
Describe how Glucose is Used to Build Proteins
-Some glucose from photosynthesis is used to make amino acids.
-To do so, glucose combines with nitrate ions and other minerals from the soil.
-The acids are built into proteins to be used as enzymes and other things for the plants survival.
-The creation of these proteins uses energy transferred from respiration
Describe the Use of Glucose as Starch
-Some glucose from photosynthesis is converted into starch to be stored.
-Starch is insoluble in water (unlike glucose) so has no effect on how water moves in and out of the plant. Because of this, plants can store a lot of starch- it is the plant’s main energy store.
-Starch is stored in the cells of leaves which provides an energy store. for when it is dark. It is also stored in tubers to help the plant survive winter.
Describe the Use of Glucose as Lipids
-Some glucose from photosynthesis and energy from respiration is used to make fats and oils.
-They can be used in cells as an energy store and sometimes is used to make the cell wall stronger.
-Lipids are also used as an energy store in seeds- they provide food for the new plant to respire as it germinates.
Describe a Method for the Photosynthesis Required Practical
-Place a boiling tube 10cm away from a light source. Now fill the boiling tube with a solution of sodium hydrogen carbonate.
-Place a piece of pondweed into the solution with the cut side at the top. Leave the pondweed for five minutes.
-Bubbles will now start to be produced from the cut end of the pondweed. Start a stopwatch and count the number of bubbles produced in one minute.
-Repeat the experiment two more times and calculate a mean value.
-Repeat the entire experiment, increasing the distance of the pondweed from the light to 20cm, 30cm, 40cm and 50cm.
Explain the Benefit of Using an LED Light Source in the Photosynthesis Required Practical
-Normal light bulbs emit a large amount of heat. This would increase the temperature of the pondweed and affect the rate of photosynthesis.
-An LED light source emits much less heat and is less likely to
change the temperature of the pondweed.
Explain why a Solution of Sodium Hydrogen Carbonate is Used in the Photosynthesis Required Practical
-Sodium hydrogen carbonate solution is a source of carbon dioxide, which the plant needs for photosynthesis.
-If we simply used water instead, then the pondweed might not have enough carbon dioxide ( carbon dioxide may be a limiting factor).
-This means that the rate of photosynthesis would be extremely slow and we would not be able to investigate how the rate of photosynthesis is affected by light intensity.
Why is the Pondweed Placed with the Cut Side On Top in the Photosynthesis Required Practical
-When the pondweed carries out photosynthesis, bubbles of oxygen gas will emerge from the cut end.
-By placing this at the top, it will be easier to count the bubbles.
-If we placed the cut end at the bottom, the bubbles could be difficult to count (for example passing behind the pondweed).
Why is the Pondweed Left for Five Minutes in the Photosynthesis Required Practical
-When we place the pondweed into the solution, it will take the pondweed a few minutes to adjust to the conditions and start to photosynthesise.
-If we counted the bubbles of oxygen produced during this
time, then we could get an inaccurate result.
-By waiting five minutes, we give the pondweed time to
acclimatise to the conditions.
What are the Problems with the Photosynthesis Required Practical
-It is difficult to count the number of bubbles of oxygen accurately. This could be difficult when the light intensity is high (when the pondweed is close to the light source) as a lot of bubbles will be produced each minute.
-The bubbles of oxygen are different sizes. This means that a tiny bubble will be counted the same as a very large bubble despite different amounts of oxygen being released.
What is the Inverse Square Law
-The inverse square law means that if the distance is halved, the light intensity will be four times greater. If you third the distance, the light intensity will be nine times greater.
-Likewise, if you double the distance, the light intensity will be four times smaller and if you triple the distance, the light intensity will be nine times smaller.
-Light Intensity ∝ 1/ distance^2
