RHS Year 1 week 9 overview 2011

RHS Level 2 Certificate

Week 9 –Photosynthesis, respiration, transpiration and nutrient and water transport

Learning outcomes

1. Photosynthesis and respiration1.1 State the basic equation for photosynthesis in words.1.2 Describe how the efficiency of photosynthesis is determined by temperature, light,

carbon dioxide, mineral nutrients and water.1.3 State the basic equations for aerobic and anaerobic respiration in words.1.4 Describe how the efficiency of respiration is determined by oxygen, water, and

temperature.2. Transportation within the plant2.1 Define the term: ‘transpiration’ and describe how water and minerals move through the

plant.2.2 Name the tissue that is involved in this process.2.3 Explain the role of xylem and phloem and describe their location within stems and

roots.2.4 Describe diffusion and osmosis and their roles within the plant, including gaseous and

liquid diffusion, transpiration, and water uptake 2.5 Describe how stomata control the release of water from the leaf.2.6 State what is meant by evaporation and how the plant may limit water loss.2.7 State the effects of relative humidity and temperature on transpiration and water loss.

Photosynthesis

Carbon dioxide +water +light → glucose + oxygen

(when in the presence of chlorophyll)

Two stages – one of which requires light and the other does not.

The photosynthetic process –light dependent phase

A molecule of chlorophyll is excited by a photon of light and an electron ‘escapes’. This energy is used to split molecules of water (H2O) into their component hydrogen and oxygen. The oxygen is released as a by-product into the atmosphere.

The energy released by breaking the chemical bonds in the water is incorporated, with the hydrogen, into energy carrying molecules called ATP and NADPH2

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Photosynthesis – light independent phase (Calvin-Benson Cycle)

The energy produced in the light dependent cycle is used in the chloroplast to convert carbon dioxide from the atmosphere into glucose (simple carbohydrate).

This phase takes place both in the day and at night – it does not need light to operate.

Limiting Factors

If a process is influenced by more than one factor, the rate of the process will be limited by the factor that is in lowest supply.

Limiting factors apply to photosynthesis and respiration

Limiting factors for photosynthesis

Light – only part of the wavelength of light from the sun is used (PAR – photosynthetically active radiation).

Carbon dioxide – more than enough of this in the open air, but under glass may become depleted.

Water –lack of water leads to the stomata closing, preventing carbon dioxide entering the leaf.

Temperature – the chemical reactions in photosynthesis are temperature sensitive. Ideal range 25°C - 36°C.

Nutrients – nutrients from the soil are needed to make chlorophyll. E.g. magnesium deficient plants photosynthesise poorly.

At low light intensity, rate of photosynthesis is proportional to light intensity.

plateau

plateau

At low CO2 concentration, rate is positively correlated with concentration

CO2 is a substrate in an enyme-catalysed light-dependent reaction.

Increased temp. gives increased energy and increased rate of photosynthesis

Optimum temperature

Above the optimum temp., enzymes are denatured and rate drops steeply.

Which enzymes are used in respiration?

Respiration – in the mitochondria

Glucose + oxygen →carbon dioxide + water+ energy

•Looks familiar? It’s the chemical equation for photosynthesis in reverse!

•Anaerobic respiration – does not use oxygen. E.g. fermentation

Carbohydrate > (enzymes) = ethanol + carbon dioxide + energy

Limiting factors of respiration

Temperature –The ideal range is 36°C (ideal) down to 0°C.

Oxygen - aerobic respiration (only) requires oxygen in sufficient concentration; reduced oxygen leads to slower respiration.

Water loss – closure of stomata due to water loss prevents oxygen from entering the plant and slows respiration.

Osmosis and diffusion

Osmosis – the movement of water molecules from an area of high water potential to an area of low water potential through a semi- permeable membrane.

Diffusion - the movement of molecules of a gas or liquid from an area of high concentration to an area of relatively low concentration.

Concentration gradient – the steeper it is the quicker the movement.

Transportation of water and nutrients

Xylem – transports water from the roots to the shoots; enters by osmosis and is drawn up by transpirational pull.

Xylem cells are long, wide and open ended; dead once mature. Linked end to end and also laterally through pores called pits

Effects of humidity and temperature on transpiration

High humidity =lower transpiration because the rate of diffusion will fall. This is why greenhouse growers damp down the floor of the greenhouse in hot weather.

The higher the temperature outside the leaf the more quickly water in the spaces in the spongy mesophyll will evaporate. The more water vapour within the leaf the faster the rate of transpiration through diffusion.

Transportation of water and minerals

Phloem – transports carbohydrates and plant growth regulators around the plant from the leaves.

Composed of sieve cells which form hollow living tubes and companion cells which provide energy to move the sap.

This active transport means that the carbohydrates can be moved to parts of the plant (such as tap root cortex) that are already rich in these substances.

Learning outcomes

1. Photosynthesis and respiration1.1 State the basic equation for photosynthesis in words.1.2 Describe how the efficiency of photosynthesis is determined by temperature, light,

carbon dioxide, mineral nutrients and water.1.3 State the basic equations for aerobic and anaerobic respiration in words.1.4 Describe how the efficiency of respiration is determined by oxygen, water, and

temperature.2. Transportation within the plant2.1 Define the term: ‘transpiration’ and describe how water and minerals move through the

plant.2.2 Name the tissue that is involved in this process.2.3 Explain the role of xylem and phloem and describe their location within stems and

roots.2.4 Describe diffusion and osmosis and their roles within the plant, including gaseous and

liquid diffusion, transpiration, and water uptake 2.5 Describe how stomata control the release of water from the leaf.2.6 State what is meant by evaporation and how the plant may limit water loss.2.7 State the effects of relative humidity and temperature on transpiration and water loss.