National 5 Biology Unit 2 – Cell Biology Section 11 Transport in Plants

We will be learning how to… Explain why multicellular organisms require transport systems Explain why plants require a transport system for water State the name for the movement of water through a plant State the structures involved in the transport of water in plants Describe the structure and function of xylem Describe the function of guard cells Describe the process of transpiration Name environmental factors which increase the rate of transpiration in plants Explain why plants require a transport system for sugar State the structure involved in the transport of sugar in plants

Plant Transport Think – What needs to be transported about inside plants? We need to find out more about how it happens and the problems that arise. http://www.twigonglow.com/films/plant-transport-1187/

Importance of transport systems Plants need transport systems to supply the raw materials for photosynthesis and to remove the products. Xylem Phloem Light Carbon dioxide Water Glucose Oxygen Chlorophyll Diffuse through stomata

Watch this clip http://youtu.be/w6f2BiFiXiM Transpiration Plants need water for photosynthesis. It is absorbed in the roots and evaporated out of leaves. Watch this clip http://youtu.be/w6f2BiFiXiM Water travels up from the roots in the xylem to the leaves. In the leaves it moves by osmosis from cell to cell and then evaporates into the gaps in the spongy mesophyll cells. If the stomata are open the water vapour will diffuse out of the leaf. This is called transpiration. http://www.twigonglow.com/films/glossary/transpiration-441/

Transpiration -water evaporates from leaves Photosynthesis produces sugar in the leaves Sugar is transported in phloem The movement of water through the plant is called the transpiration stream stem roots Water and ions pass up xylem Mineral ions enter by active transport Water enters roots by osmosis National 4/5 Biology Course Unit 2

Transpiration - Transport of Water lignin xylem vessel

Long root hair to increase surface area Root Hair Cell Structure Long root hair to increase surface area Function Collects water and mineral nutrients present in soil to transport this to the rest of the plant

Xylem The role of the xylem is to transport water from the roots to all other areas of the plant. The xylem plays an important role in the transport of minerals which are dissolved in the water. It also helps strengthen the stem of the plant. National 4/5 Biology Course Unit 2

Xylem They have no cell contents and no nucleus. They are hollow tubes of dead cells. The end walls have broken down and have disintegrated. Side walls are strengthened by lignin to prevent damage by water pressure

The Structure of a Leaf Leaves Leaves are adapted for photosynthesis by having a large surface area, and contain stomata (openings) to allow carbon dioxide into the leaf. These design features can result in the leaf losing a lot of water. The cells inside the leaf have water on their surface. Some of this water evaporates, and the water vapour can then escape from inside the leaf by diffusion. To reduce loss the leaf is coated in a wax cuticle to stop the water vapour escaping through the epidermis. Leaves usually have fewer stomata on their top surface to reduce this water loss.

the protective outer layer of cells on the surface of a leaf. Structure Function Epidermis the protective outer layer of cells on the surface of a leaf. Palisade Mesophyll elongated cells located under the epidermis. contains most of the leaf’s chlorophyll. Spongy Mesophyll located below the palisade mesophyll. irregularly-shaped cells with many air spaces between. contains some chlorophyll. Vein contains a collection of xylem and phloem vessels. Moist air space gases dissolve in water vapour for photosynthesis. Guard cells control the opening and closing of stoma. Stoma openings in the surface of a leaf for gas exchange.

Stomata and Guard Cells Turgid – full of water – stoma is open Flaccid – stoma is closed Guard cells surround each stoma. They regulate the rate of transpiration by opening and closing the stomata as the water is used up Thin outer wall stretches more than thick inner wall Walls not stretched

Transpiration Rate light temperature humidity wind Various factors will affect the rate of transpiration. This includes light temperature humidity wind

Using a Potometer – Measuring Transpiration

Phloem As well as transporting water and minerals, plants have to transport the sugar from photosynthesis from the leaves to other parts of the plant. This is carried out by special cells called phloem. National 4/5 Biology Course Unit 2

Phloem Columns of sieve tubes, connected by sieve plates at either end. sieve tube Companion cells sit next to the sieve tubes. companion cell They have a dense cytoplasm and a nucleus. They are living cells. sieve plates with pores nearby cell

Stem Cross Section

Root Cross Section

Glossary Xylem transport water from the roots to all other areas of the plant. Root Hair Cell Collects water and mineral nutrients present in soil to transport this to the rest of the plant Lignin Structural material that supports the xylem tissues by lining the cell wall Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump. Potometer a device used for measuring the rate of water uptake of a leafy plant shoot. The main reason for water uptake by a cut shoot is transpiration (evaporation in plants) and is affected by the transpiration stream Upper Epidermis Thin layer to allow more light to reach the palisade cells Mesophyll Layer Contains many chloroplasts to absorb all the available light Vein a vascular structure (xylem and phloem cells surrounded by the bundle sheath) in a leaf that provides supports for the leaf and transports both water and food Stoma A pore that is used for gas exchange. They are mostly found on the under-surface of plant leaves.

Glossary Guard Cells These help to regulate the rate of transpiration by opening and closing the stomata Moist air space Increases surface area of leaf to absorb more carbon dioxide Turgid swollen Flaccid oft and hanging loosely or limply Phloem transports glucose from the leaves to the rest of the plant Sieve Plates pores in the plant cell walls that facilitate transport of materials between them Sieve Tubes living cells of the phloem, the nuclei have fragmented and disappeared and the end walls of which are pierced by sieve-like groups of pores (sieve plates). They transport sugar. Companion Cell It regulates the activity of the adjacent sieve tube and to take part in loading and unloading sugar into the sieve plate