Red Hunting – Topic 4 Transport in Plants

Describe and explain the structure of xylem and phloem tissues in relation to their role in transport. Explain how water can be moved through plant cells by the apoplastic and symplastic pathways. Explain how the cohesion-tension model explains the transport of water from plant roots to shoots. Explain how temperature, light, humidity and movement of air affect the rate of transpiration. Explain the strengths and weaknesses of the mass-flow hypothesis in explaining the movement of sugars through phloem tissue. CORE PRACTIAL 8: Describe how to investigate factors affecting water uptake by plant shoots using a potometer.

On the white boards describe the structure of the phloem and xylem. Describe and explain the structure of xylem and phloem tissues in relation to their role in transport. Starter On the white boards describe the structure of the phloem and xylem.

Explain how water can be moved through plant cells by the apoplastic and symplastic pathways.

Xylem Dead cells and have thick, lignified secondary walls – Prevents collapse No cytoplasm (less resistance to flow of water) Attached end to end to form continuous elements. Spiral thickening of xylem tissue to support growth

On the white boards, briefly outline what is happening at A, B and C Explain how the cohesion-tension model explains the transport of water from plant roots to shoots. On the white boards, briefly outline what is happening at A, B and C

Types of water movement Explain how the cohesion-tension model explains the transport of water from plant roots to shoots. Types of water movement

Phloem

Movement of organic molecules in plants Organic molecules move via the phloem in plants. Unlike the xylem, phloem is made up of living cells. Sieve tube members and their companion cells. Sieve tube members are connected to one another by sieve plates to form sieve tubes. Companion cells are actually connected to their sieve tube members by plasmodesmata.

Pressure-flow hypothesis Watch the video clip carefully. You will be expected to explain the pressure-flow hypothesis in your own words.

Transport in the phloem Happens in all directions From source to a sink Source = plant organ that is a net producer of sugar by photosynthesis or hydrolysis of starch. Leaves are primary sugar sources. Sink = Plant organ that uses or stores sugar, roots, buds, stems, seeds and fruits are all sugar sinks. Some structures (bulbs) can be a source and a sink.

Pressure flow hypothesis

19. Outline the role of the phloem in the active translocation / mass-flow hypothesis of biochemicals. (Total 5 marks)

19. Outline the role of the phloem in the active translocation of biochemicals. (Total 5 marks) living tissue; composed of companion cells / sieve tube members; companion cells involved in ATP production; sucrose / amino acids / assimilate / products of photosynthesis transported; bi-directional transport; source / leaves to sink / fruits / roots / storage organs / named storage organ; pressure flow hypothesis / movement of water into phloem causes transport;

Transpiration http://www.biologymad.com/resources/transpiration.swf

Virtual experiment We are going to carry out a virtual experiment as a class – first we will look at the real equipment

Explain Watch the practical being carried out on the board and complete the worksheet.

In your own words… Describe and explain why the following increase the rate of transpiration: Light Temperature Wind Humidity (how moist the air is)

Light - Transpiration The more light there is the more PHOTOSYNTHESIS will take place. The stomata will open WIDER to allow more CARBON DIOXIDE in. The plant will also need more WATER so more water enters and more water leaves.

Temperature - Transpiration The higher the temperature the faster the water molecules are moving, this speeds up the RATE of transpiration. This is the same for WINDY conditions.

Humidity - Transpiration If the air is very DRY on the outside, water will move from a high concentration to a low concentration…. Likewise, if the air is very WET (HUMID) less water will leave the leaf.

The evaporation of water into the atmosphere, from the leaves and stems of plants, through the stomata, draws water up the plant. Water and minerals are collected at the roots and carried through the plant by xylem.