Plants & Photosynthesis (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards

Root hair cells have long extensions that increase the surface area of the root, which increases the rate of water absorption by osmosis from the soil.

Mineral ions are taken up by root hair cells from the soil by active transport, while water is absorbed by osmosis.

False.

Magnesium ions are needed to make chlorophyll. Nitrate ions are needed to make proteins.

Diffusion, osmosis and active transport are too slow to meet all of a large organism's needs. A transport system moves substances such as water, mineral ions and sugars between organs efficiently.

During photosynthesis, carbon dioxide diffuses into the leaf and oxygen diffuses out of the leaf.

At night, only respiration occurs. Oxygen diffuses into the leaf (it is used in respiration) and carbon dioxide diffuses out of the leaf, both moving down their concentration gradients.

True.

Root hairs are single-celled extensions that greatly increase the surface area of the root, improving absorption of water by osmosis and mineral ions by active transport.

Transpiration is the process by which water evaporates from the surfaces of plant leaves and diffuses out through the stomata as water vapour, creating a continuous flow of water up through the plant.

True.

When water moves into the guard cells by osmosis, they become turgid, pulling apart and opening the stomatal pore to allow gas exchange and water loss.

The transpiration stream is the continuous upward movement of water through the xylem, from the roots to the leaves, driven by the evaporation of water from the leaf surface.

The rate of transpiration increases with higher temperature, higher light intensity, and increased air movement.

Higher temperature increases the rate at which water evaporates from the surface of mesophyll cells inside the leaf, so water vapour diffuses out through the stomata more quickly.

False.

Xylem only transports water and mineral ions in one direction — upwards from roots to leaves. It is phloem that transports sugars in both directions.

When guard cells lose water by osmosis to neighbouring cells, they become flaccid, causing the stomatal pore to close. This prevents further water loss when water availability is low.

In the leaves, water evaporates from mesophyll cells and is lost through stomata as water vapour.

High light intensity causes the stomata to open wider, which increases the rate of water vapour diffusing out of the leaf, so the overall rate of transpiration increases.

Chromatography is a technique used to separate and identify the components of a mixture. It uses a mobile phase (solvent) and a stationary phase (e.g. paper) to separate substances based on their different solubilities.

False.

The baseline must be drawn in pencil because ink would dissolve in the solvent and run up the chromatography paper along with the sample, interfering with the results.

The mobile phase is the liquid solvent that carries the sample up the paper.

The stationary phase is the chromatography paper itself, which does not move.

R_f = distance moved by substance ÷ distance moved by solvent

A pure substance produces only one spot on the chromatogram, because it contains only a single compound that travels a fixed distance in the given solvent.

False.

The R_f value of a substance depends on the solvent used. Changing the solvent changes the R_f value, so the same solvent must be used when comparing R_f values.

A more soluble substance spends more time in the mobile phase (solvent) and is carried further up the paper. Less soluble substances spend more time in the stationary phase and travel a shorter distance.

An R_f value (retention factor) is the ratio of the distance moved by a substance to the distance moved by the solvent. It is always less than 1 and has no units.

An impure substance will produce multiple spots on a chromatogram, while a pure substance produces only one.

To investigate how paper chromatography can be used to separate and identify a mixture of food colourings, and to calculate R_f values for each component.

True.

The baseline must sit above the solvent level. If the baseline is submerged, the samples will wash off into the solvent rather than being carried up the paper.

In paper chromatography, the solvent travels up the paper by capillary action, carrying the food colouring spots with it.

Ink from a pen would dissolve in the solvent and run up the chromatography paper, interfering with the results. Pencil does not dissolve, so it stays in place.

False.

The R_f value is a ratio of two distances, so the units cancel. R_f values are unitless and always have a value less than 1.

Calculate the R_f value of each spot in the unknown sample. Compare these values with the R_f values of known food colourings run under the same conditions. A match in R_f value indicates the same substance.

After the chromatography run, a pencil line is drawn at the solvent front to mark how far the solvent has travelled.

It suggests that the unknown mixture U contains the same substance as known colouring A, since the same compound has the same R_f value under the same conditions.

Photosynthesis is an endothermic reaction in which plants use light energy, carbon dioxide and water to produce glucose and oxygen. It takes place in the chloroplasts of plant cells.

False.

Photosynthesis is an endothermic reaction — it transfers energy from the environment (in the form of light) to the plant. Energy is stored in the glucose produced.

Carbon dioxide + water → glucose + oxygen

Light energy is required for this reaction to occur.

Glucose produced in photosynthesis can be used for respiration, converted to insoluble starch for storage, or used to make cellulose which strengthens cell walls.

Plants are called producers because they make their own food (glucose) using light energy through photosynthesis, rather than consuming other organisms.

False.

Plants convert excess glucose into insoluble starch for storage. Starch is insoluble, which means it does not affect the water potential of cells.

1. To produce cellulose for strengthening cell walls.

2. To produce fat or oil for storage (especially in seeds).

3. Combined with nitrate ions to make amino acids for protein synthesis.

(Any two)

To make amino acids for protein synthesis, plants combine glucose with nitrate ions absorbed from the soil.

Most photosynthesis takes place in the leaves, in mesophyll cells that are packed with chloroplasts containing chlorophyll to absorb as much light energy as possible.

True.

Chloroplasts are the organelles where photosynthesis occurs. They contain chlorophyll, the pigment that absorbs light energy to drive the photosynthesis reaction.

A limiting factor is any condition that, when in short supply, slows the rate of photosynthesis. The three main limiting factors are light intensity, carbon dioxide concentration, and temperature.

False.

Although water is a raw material for photosynthesis, it is not a limiting factor because the amount needed is small compared to how much is transpired, so there is rarely a shortage.

At very high temperatures, the enzymes controlling photosynthesis become denatured — the active site changes shape and is no longer complementary to its substrate, so the reaction can no longer proceed.

As light intensity increases, the rate of photosynthesis increases until another limiting factor prevents the rate from rising further.

The rate of photosynthesis does not increase significantly because temperature is now the limiting factor — increasing a non-limiting factor has no effect on the rate.

True.

The inverse square law states that light intensity is proportional to 1/d², so when the distance doubles, the light intensity decreases by a factor of four (2² = 4).

The inverse square law states that light intensity is inversely proportional to the square of the distance from the source: light intensity ∝ 1/d². Doubling the distance reduces light intensity to a quarter of its original value.

In a greenhouse, farmers carefully control levels of heat, light and carbon dioxide to maximise the rate of photosynthesis, but must avoid spending money on a factor that is not the limiting factor.

Once carbon dioxide concentration rises above the level at which it limits photosynthesis, another factor (such as light or temperature) becomes the limiting factor, so extra CO₂ has no effect on yield and the cost is wasted.

The aim is to investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed.

In the pondweed experiment, the rate of photosynthesis is measured by counting the number of bubbles produced by the plant per minute as the distance from the lamp changes.

False.

Moving the lamp further away decreases light intensity, which reduces the rate of photosynthesis — fewer bubbles of oxygen are produced per minute.

The glass tank of water acts as a heat filter, preventing the lamp from heating the water around the plant. This ensures that temperature is controlled as a variable and does not affect the results.

The independent variable is the factor deliberately changed by the investigator. In the pondweed experiment, it is the distance of the lamp from the pondweed, which alters the light intensity reaching the plant.

True.

Repeating measurements and calculating a mean reduces the effect of random errors and improves the reliability of the results.

A more accurate way to measure gas production in the pondweed experiment is to use a gas syringe to collect the volume of oxygen produced, rather than counting bubbles.

The number of bubbles per minute increases because the light intensity is greater, providing more energy for photosynthesis and so more oxygen is produced.

Translocation is the transport of dissolved sugars and other soluble products of photosynthesis through the phloem from sources (where they are made) to sinks (where they are used or stored).

False.

Phloem is made of living, elongated cells. It is xylem that is made of dead cells. This difference is important for the function of each tissue.

The main sugar transported in the phloem is sucrose, which is dissolved in cell sap and moves from sources (such as leaves) to sinks (such as roots or growing tissues).

In translocation, substances move from a source (where they are made) to a sink (where they are used or stored) through the phloem.

Sieve plates are perforated end walls found between phloem cells. Their pores allow cell sap containing dissolved sugars and other substances to flow freely between adjacent phloem cells during translocation.

True.

In winter, storage organs act as sources and release sucrose and amino acids into the phloem so that other parts of the plant can continue respiration.

Phloem cells are joined end to end, and their end walls contain sieve plates with pores. These pores allow cell sap containing dissolved sugars and nutrients to pass freely from one cell to the next.

After a period of growth, leaves act as the source and roots act as sinks, storing sucrose as starch.

A communicable disease is a disease caused by a pathogen that can be transmitted (spread) between individuals within a population. Both plants and animals can be affected.

TMV is caused by a virus. It is a widespread plant pathogen affecting approximately 150 species of plants, including tomatoes and cucumbers.

True.

Tobacco mosaic virus (TMV) produces a distinctive mosaic pattern of discolouration on the leaves, which reduces the plant's ability to photosynthesise and stunts growth.

Rose black spot is a fungal disease in which purple or black spots develop on the leaves of roses. Affected leaves often turn yellow and drop early, reducing the plant's ability to photosynthesise.

Rose black spot is spread through the environment by water or wind, and can be treated using fungicides or by removing affected leaves.

Rose black spot causes leaves to develop black spots, turn yellow, and fall early. This reduces the leaf area available for photosynthesis, so the plant produces less glucose for growth.

False.

Rose black spot is caused by a fungus, not a virus. It is treated with fungicides or by removing and destroying the affected leaves.

Tobacco mosaic virus affects the growth of a plant because the mosaic pattern on the leaves reduces the plant's ability to carry out photosynthesis.

Plant diseases can be spread by:

1. Water (e.g. splashing rain carrying fungal spores)

2. Wind (e.g. carrying spores or viral particles between plants)