1 of 40 Boardworks Ltd 2007 2 of

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How do plants get what they need? What do plants need for healthy growth? l minerals l water l sunlight l oxygen for respiration l carbon dioxide for photosynthesis Where do plants get these nutrients? Like all organisms, plants have to get materials for growth from their environment. Plants must then get these nutrients to the part of the plant that needs them. 3 of 40 © Boardworks Ltd 2007

Moving materials How do plants transport materials to where they are needed? 4 of 40 © Boardworks Ltd 2007

How are plants adapted for transport? The structures of cells and tissue in different parts of the plant are adapted to allow transportation of essential materials. Leaves are entry and exit points for the gases needed by plants. Stems connect the roots to the leaves, flowers and fruits. They contain cells specially adapted for transportation of water, minerals and sugars. Roots absorb water and minerals from the soil. 5 of 40 © Boardworks Ltd 2007

What are the functions of plant parts? 6 of 40 © Boardworks Ltd 2007

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Which cells transport nutrients? Plants contain two types of cell adapted for transportation. Xylem cells transport water and minerals up the stem from the roots to the shoots and leaves. This transport occurs in one direction only. Phloem cells transport sugars produced in the leaves up and down the stem to growing and storage tissues. The cells are arranged in plants as vascular bundles. Both phloem and xylem form continuous systems connecting roots, stems and leaves. 8 of 40 © Boardworks Ltd 2007

Inside a plant stem 9 of 40 © Boardworks Ltd 2007

What are vascular bundles? 10 of 40 © Boardworks Ltd 2007

How is xylem adapted for transportation? Water and minerals travel in xylem vessels. Xylem vessels have thick cellulose cell walls, strengthened by lignin. The inside of the cell is hollow. Xylem vessels are dead cells. Xylem vessels transport water and minerals from the roots to the shoot and leaves. This transport only occurs in one direction. The thick walls of xylem cells also help support plants. 11 of 40 © Boardworks Ltd 2007

How is phloem adapted to transportation? Phloem is made of columns of living cells. They transport food, in the form of sugars. Sugars are carried from the leaves to the growing and storage parts of the plants. This movement takes place in both directions. Phloem cells are also called sieve tubes. Cells are joined by small holes in the cell wall at the end of each cell, forming a continuous system. The end cell walls are called sieve plates. 12 of 40 © Boardworks Ltd 2007

Cells in the vascular bundles 13 of 40 © Boardworks Ltd 2007

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Do plants produce waste? All animals eat food to survive. Not all of the food can be used by the body, so eventually some will exit the body as waste. Plants are different from animals because they produce their own food through the process of photosynthesis. Does this mean they do not produce any waste? Oxygen is made during photosynthesis but not all of it is used by the plant. It is a waste product. How is it removed from the plant? 15 of 40 © Boardworks Ltd 2007

How do gases move in and out of plants? Plants use carbon dioxide during photosynthesis and produce oxygen. These gases move in and out of the plant through the leaves by diffusion. When the concentration of carbon dioxide inside the plant is low, it will diffuse in from the air, through pores in the leaves into the plant cells. If the concentration of oxygen is high inside the plant, it will diffuse from the plant cells through the pores and into the air. 16 of 40 © Boardworks Ltd 2007

How are leaves adapted for diffusion? The diffusion of gases occurs in the leaves. They are adapted for this function in the following ways: l Leaves are thin. This decreases the distance gases have to travel between the air and cells. l There air spaces between cells. This increases the speed of diffusion from the air to the cells inside the leaf. l There are lots of stomata (pores) on the undersides of leaves. These let gases in and out. 17 of 40 © Boardworks Ltd 2007

What are stomata? On the underside of leaves are small holes, or pores, called stomata. A single hole is called a stoma. Each stoma is surrounded by two guard cells, which control the opening and closing of the stoma. When carbon dioxide levels are low inside the plant, the guard cells gain water and become turgid. They curve out, opening the stoma and allowing gases in and out. Water also evaporates through stomata. High carbon dioxide levels cause the guard cells to lose water, closing the stoma. What would happen if the stomata were permanently open? 18 of 40 © Boardworks Ltd 2007

Opening and closing of stoma 19 of 40 © Boardworks Ltd 2007

Diffusion of gases 20 of 40 © Boardworks Ltd 2007

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How do tall trees get enough water? Redwoods are the tallest species of tree in the world. The tallest redwood ever measured was 120 metres tall. That is six times the height of the Angel of the North! How does a plant this size get water from its roots to the branches at the top? The water will travel up the stem, or trunk, of the tree. What experiment could show that water travels up stems? 22 of 40 © Boardworks Ltd 2007

Movement of water up a stem 23 of 40 © Boardworks Ltd 2007

What is transpiration? Transpiration is the loss of water by evaporation from plants. Plants lose water when they open the stomata in the leaves to let in carbon dioxide. Water always moves from an area of high concentration to an area of low concentration. This movement of water is a type of diffusion called osmosis. Air around the plant usually contains less water than the cells of the plant, so water evaporates into the air. Although it may seem bad for plants, transpiration actually moves water from the roots to the top of the plant, without using energy. How does this work? 24 of 40 © Boardworks Ltd 2007

Transpiration 25 of 40 © Boardworks Ltd 2007

Is the rate of transpiration constant? Transpiration is a bit like a straw, pulling water up the plant. Sometimes the pulling force will be stronger and the plant will lose more water. The speed at which a plant loses water is called the rate of transpiration. This varies depending on the plant’s environment. What environmental factors will affect the rate of transpiration? l humidity (amount of moisture in the air) l light intensity l temperature l air movement (wind). 26 of 40 © Boardworks Ltd 2007

Why does transpiration vary? 27 of 40 © Boardworks Ltd 2007

How is the rate of transpiration measured? Transpiration can be measured using a potometer. A cut plant stem is sealed into the potometer using a rubber bung. An air bubble is introduced to the capillary tube. The distance the bubble travels shows how much water the stem has taken up. This gives an indirect measurement of the rate of transpiration. 28 of 40 © Boardworks Ltd 2007

Transpiration – true or false? 29 of 40 © Boardworks Ltd 2007

How are roots adapted to their function? The roots of this hyacinth bulb are long and thin. They have formed a fine network, filling the available space. Roots contain thousands of tiny root hair cells, which project out into the soil. How do these features make roots suitable for absorbing water and minerals? l high surface area to volume ratio l maximum contact with the soil l firm anchorage. 31 of 40 © Boardworks Ltd 2007

How do minerals enter plants? Like water, minerals enter plants through the roots. However, they do this by different methods. Water passively diffuses with a concentration gradient from the soil into the roots and up the stem. Minerals are usually found in the soil in lower concentrations than they occur in the plant. Why can they not be transported by diffusion? Diffusion cannot take place against a concentration gradient. Instead, minerals enter the roots by active transport. 32 of 40 © Boardworks Ltd 2007

What is active transport? Active transport uses energy from respiration to move substances against a concentration gradient. soil root hair cell Specific minerals from the soil enter through channels in the cell walls of the root hair cells. The minerals then travel around the plant in the xylem vessels. Plants may take up some minerals in the soil but not others. Why is it important that plants select which minerals to transport? 33 of 40 mineral © Boardworks Ltd 2007

Active transport 34 of 40 © Boardworks Ltd 2007

Transporting minerals – activity 35 of 40 © Boardworks Ltd 2007

Glossary (1/2) l active transport – The movement of a substance from an area of low concentration to high concentration. l concentration gradient – A change in the concentration of a substance from one area to another. l cellulose – The main component of cell walls. l diffusion – The movement of a substance from an area of high concentration to low concentration. l guard cells – A pair of cells that control the opening and closing of a stoma (single hole). l humidity – The amount of water vapour in the air. l lignin – A substance found in some xylem cells, which strengthens the cell wall. l osmosis – The movement of water from an area of high concentration to low concentration. 37 of 40 © Boardworks Ltd 2007

Glossary (1/2) l phloem – Plant tissue that transports food. l potometer – A piece of equipment that can be used to indirectly measure the rate of transpiration. l root hair cell – A thin, hair-like outgrowth on roots. l transpiration – The evaporation and diffusion of water from leaves into the air. l sieve tube – A series of joined phloem cells. l stoma (singular) – A single hole on the lower surface of the leaf that allows gases in and out. l stomata (plural) – Small holes in the lower surface of a leaf that allow gases in and out. l vascular bundle – A grouping of transport tissues. l xylem – Plant tissue that transports water and minerals. 38 of 40 © Boardworks Ltd 2007