Unit 6 :plant nutrition + Unit 8: transport in plants Flashcards
(28 cards)
What is photosynthesis + equation?
The process by which green plants make carbohydrates from raw materials (carbon dioxide and water) using energy from light. A reaction that takes in energy.
Word equation: carbon dioxide + water -> (light) glucose + oxygen
Balanced chemical equation: 6CO2 + 6H2O -> C6H12O6 +6O2
What is chlorophyll?
A green pigment found in the chloroplast of plant cells. It absorbs light energy (which is converted into the chemical energy of glucose molecules)
In what form is glucose (produced during photosynthesis) stored or transported?
Sucrose (carbohydrate molecule that is used by plants as a store of chemical energy) because glucose molecules are very reactive (so this prevents unwanted reactions). It is then transported like this via the phloem to different parts of the plant. It is used for growth of shoots, young leaves, roots and fruits.
It is also converted into starch and stored in the chloroplast & cytoplasm (energy store).
3 uses of carbohydrates in plants
- Energy source - some of the glucose produced during photosynthesis is broken down during respiration to release energy
- Structural support - some glucose is converted into cellulose, an important component of plant cell walls.
- Assist pollination - nectar, a sweet sugary liquid, is made from glucose which attracts pollinators (insects, birds, etc)
What are minerals?
Inorganic substances that are essential to organisms to allow them to carry out various functions. E.g. magnesium nitrate. They are formed in soil by the natural breakdown of rocks. Though many are insoluble, soluble minerals may be used by plants because they break down to form charged particles called mineral ions which can then be absorbed by the root hair cells in plant roots.
Name and explain the use of 2 mineral ions
- Magnesium ions - used for making chlorophyll (one ion at the center of a chlorophyll molecule.
- Nitrate ions - used for making amino acids which are in turn used to make the proteins plants need,
How to detect when photosynthesis has occurred?
The presence of starch is one indication (since glucose produced during photosynthesis is stored as starch in leaves). Plants must be destarched (left in dark cupboard for 24hrs).
1. Place leaf in beaker of boiling water for 30sec
2. Remove leaf & turn off bunsen burner
3. Place leaf in test tube of alcohol solution until all the green colour is gone
4. Remove leaf and dip it into hot water to soften it and remove excess alcohol
5. Place the leaf on a white tile and cover it with iodine solution. Observe any colour changes, the areas that turn blue-black have starch present.
What is a variegated plant?
A plant whose leaves have both green and non-green parts (e.g. white or yellow) so some parts have no chlorophyll.
How can the importance of chlorophyll for photosynthesis be tested?
- Destarch a variegated plant.
- Place a plantin a warm, sunny area for 48hrs
- Test the leaves using the starch test.
Parts of the leaf that were green should become blue-black when iodine is added, while non-green areas shouldn’t change in colour. This shows that parts of the variegated leaf without chlorophyll do not produce starch, which means that photosynthesis does not happen when there is no chlorophyll.
How to test the importance of carbon dioxide for photosynthesis?
- Destarch a plant with green leaves
- Pour 50ml of potassium hydroxide (KOH) into a conical flask
- Put 1 leaf into the flask but above the KOH
- Place the plant and the flask in a sunny place for 48hrs
- Do the starch test to check whether photosynthesis has occurred
Results: the leaf placed above the KOH solution should not have had a color change because KOH absorbs carbon dioxide, so no starch was produced because photosynthesis did not occur.
How to test the necessity of light for photosynthesis?
- Destarch a plant with green leaves
- Use a paper clip to wrap aluminium foil around a part of a leaf (still attached to plant)
- Leave the plant in a sunny place for a couple hours
- Remove aluminium foil and do the starch test.
There will be no colour change in the part of the leaf that was covered because photosynthesis did not occur there, therefore starch was not produced.
State and explain the 3 factors which affect the rate of photosynthesis
- Light intensity - increasing light intensity increases the rate of photosynthesis until a certain point, after which the rate of photosynthesis will remain the same. Different light intensities can be achieved by planing the light source closer/farther from the plant.
- Carbon dioxide concentration - increasing the CO2 concentration will increase the rate of photosynthesis until a certain point, after which the rate of photosynthesis will remain the same. Different CO2 concentrations can be achieved by using different concentrations of sodium bicarbonate (NaHCO3) solution.
- Temperature - the process of photosynthesis is controlled by enzymes, which have an optimal temperature. Raising the temperature to 20-30 degrees (usually optimal range) will increase the rate of photosynthesis but raising it higher will decrease it due to the denaturation of enzymes.
Describe the effect of light on gas exchange
Aerobic respiration is constantly happening in plants, and it releases carbon dioxide which photosynthesis is only happening when light is present and it releases oxygen. Therefore, at low light intensities, the plants overall release CO2 while at high light intensities they overall release oxygen.
This can be shown in an experiment using hydrogen-carbonate indicator and aquatic plants. In dark conditions, when the HCO3 is added to the water, it will turn orange/yellow, indicating high CO2 concentration, while in light conditions, it will turn magenta/purple indicating low CO2 concentrations. If the rate of photosynthesis is equal to the rate of respiration, the HCO3 will turn red, representing normal atmospheric concentration of CO2.
State and explain 2 leaf adaptations
- Large surface area - exposes larger area to sunlight & air and helps the absorption of these materials
- Thin - ensures that CO2 from the air diffuses quickly into photosynthetic cells. Thinness also helps light penetrate them easily.
What is a dicotyledonous plant?
Typical broad-leaved flowering plant.
State the name, function & adaptation of each leaf cell structure from top to bottom
- Cuticle - a waxy, transparent layer which stops water from evaporating from the leaf & enables maximum light penetration.
- Upper epidermis - thin layer which protects the inner cells, and has no chloroplast (transparent) which lets light pass through for photosynthesis
- Palisade mesophyll layer - a tissue made of tightly-packed box-shaped cells, each of which have lots of chloroplast, pushed to the edges of the cell by a large vacuole so they can absorb more light. Chloroplast is the site of photosynthesis because it has chlorophyll which absorbs light, as well as enzymes needed for photosynthesis.
- Spongy mesophyll - the site of gas exchange due to its loosely packed cells creating air spaces to allow diffusion of gases throughout the leaf
- Vascular bundle - contain the xylem and phloem tissue
- Lower epidermis - thin layer which protects the inner cells, and has no chloroplast which lets light pass through for photosynthesis (apart from guard cells)
- Stomata - openings whose size controls the diffusion of water vapor & gases in and out of the leaf
- Guard cells - work in pairs to control the size of the stomata opening. The entry & loss of water by osmosis results in changes to their shape, which in turn leads to the opening/closing of the stomata
Explain the functions and adaptations of both tissues in the vascular bundle
- Xylem - tissue made of dead cells which forms hollow, waterproof tubes. It carries water and mineral ions from the roots to the leaf. Provides support for plant and keeps it upright due to thick walls.
- Phloem - tissue made of sieve tubes and companion cells (which provide energy for transport). Carries sucrose & amino acids away from the leaf
Describe the positions of the xylem & phloem in different parts of the plant
Root - big cross in the middle with larger opening: xylem; the smaller parts around it but still within the circle: phloem
Stem - 3 different semi-circles pointing outwards, around a honeycomb-like structure; the closest one to the center is the xylem; the middle one if the phloem;
Leaf - at the top of vascular bundle: xylem; at the bottom: phloem
Remember: xylem - inside, phloem - outside
What are root hair cells?
Specialized cells found on the surface of plant roots. They have long hair-like structures. Their function is to increase surface area of the roots for increased absorption of mineral ions and water from the soil. They also have a lot of mitochondria to release energy for active transport.
Describe the pathway that water takes from the roots to the leaves
Root hair cell (surface of root) -> root cortex cell (inside root) -> xylem vessels (from the roots through the stem) -> mesophyll cells (in leaf)
What is transpiration + purpose?
The loss of water vapour from the leaves. The water (from the soil, transported to the spongy mesophyll cells) will evaporate at the surface of spongy mesophyll cells (due to the air spaces in them & a large sa), and then the water vapour will then diffuse out of the leaf through the stomata. Leaves have more stomata in the lower epidermis, which means hat most transpiration happens there.
State 1 advantage and 1 disadvantage of transpiration
+ helps cool the plant on hot days as water evaporates
- plant may lose too much water
State 3 factors which affect the rate of transpiration
- Temperature - higher temperature means higher rate of transpiration to cool down the plant. At high temperature, water molecules gain energy, the rate of evaporation of water from mesophyll cells increases, and therefore diffusion of water vapour increases.
- Wind speed - higher wind speed will take away water vapour from the surface of leaves, which means a higher concentration gradient so faster diffusion so higher rate of transpiration
- Humidity - as humidity increases the leaf is surrounded by moist air, so the concentration gradient decreases resulting in less transpiration.
Describe an experiment investigating transpiration
- Cut a small shoot off a plant
- Set up a potometer (a capillary tube is connected to both the beaker of water and the leaves of the shoot. As water vapour from the leaves is lost by transpiration, it is replaced by water from the beaker, which causes the air bubble in the capillary tube to move, the distance of which is recorded) with the cut shoot
- Place the apparatus in a cool room
- Record the temperature of the room.
- Measure the time taken for the bubble in the capillary tube to move a given distance.
- Repeat steps 4 and 5 in a warm room, then in a hot room.
Same thing can be done to test the effects of wind speed and humidity
