Planet Earth and Its Environment A 5000-million year Journey

Part of the Patterns in Nature ModuleBiology in Focus, Preliminary CourseGlenda Childrawi and Stephanie HollisPatterns in NatureTopic 11: Autotrophs Obtaining EssentialsDOT PointsExplain the relationship between the organisation of the structures used to obtain water and minerals in a range of plants and the need to increase surface area available for absorption.

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IntroductionRoots are the structures in plants for absorbing water and inorganic minerals. These structures have an extensive surface area which allows these substances to be absorbed efficiently.

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Water UptakePlants need to absorb large quantities of water at a high rate to maintain their water balance. The uptake of water occurs by the process of osmosis.

When water in the soil is at a higher concentration than the cell sap of root cells, water will move from the soil into the root by osmosis.

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revisionworld.co.ukWater UptakeThis is a passive form of transport and occurs slowly, so it is essential that the surface area of structures involved in absorption is increased.

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Mineral UptakeThe uptake of inorganic mineral salts is mainly by the process of diffusion. If the minerals are in a higher concentration in the soil than they are in the cells of the roots they will move passively into the roots.

If diffusion alone is inadequate, facilitated diffusion and active transport may also be involved.

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Increased Surface AreaThe uptake of both water and mineral salts depends on a large area of contact between the roots and the soil water containing the dissolved minerals. An increased surface area in roots is achieved in the following ways:Root hair zoneExtensive branching Nature of cells

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Increased Surface AreaRoot Hair Zone:The root hair zone is in the younger part of each root, near the tip. In this region, the epidermal cells protrude outwards into the surrounding soil as microscopic extensions called root hairs.

Their presence increases the surface area of a root up to 12 times!

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Increased Surface AreaExtensive BranchingExtensive branching of root systems in the mature regions increases the surface area of the root for absorption.

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Increased Surface AreaNature of CellsWater enters the root through the epidermal cells across the entire surface of the root system. The flattened nature of these cells increases their exposed surface.

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Movement of water and mineralsWater and minerals that enter the root through the epidermal cells, particularly through the root hair zone, move across the root to the water conducting tissue called xylem, found in the centre of the root.

Water moves by osmosis through the cells.

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Movement of water and mineralsThe water and minerals then move across the cortex, along a gradient, into the central vascular tissue.

The vascular tissue in the centre of the root is continuous, passing up the stem and into the leaves as veins in the leaf, serving as the main transport tissue in the plant.

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Movement of water and mineralsVeins are made of two types of tissue: xylem and phloem.Xylem transports water and dissolved minerals to the leafPhloem transports sugars made in the leaves to the rest of the plantextension.oregonstate.edu

DOT PointsExplain the relationship between the shape of leaves, the distribution of tissues in them and their role.

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The Role of LeavesLeaves are the main photosynthetic structures in plants. Their primary function is to absorb sunlight and make food. They also carry out the function of transpiration.enchantedlearning.com

The Role of LeavesLeaves are structurally adapted to enable them to effectively function. They are made up of a number of different tissues, arranged in a highly organised way to maximise their efficiency. flickr.com

The Role of LeavesThe structural features needed by a leaf to effectively photosynthesis are:Large surface area, with an outer layer able to absorb light and carbon dioxidePores in the leaf surface for the exchange of gases with the environmentCells inside that contain chloroplasts to trap energyA water transport system from the roots to the leavesA food transport system from the leaves to other parts of the plant. The Role of LeavesLeaves have an enormous diversity of shapes and sizes, but most are flattened in shape and relatively thin, resulting in a large surface area that is exposed to the sun.

This allows the maximum absorption of light for photosynthesis

hiltonpond.orgThe Role of LeavesThe surface of leaves is covered by a protective layer of cells, the epidermis. These epidermal cells protect the inner tissues and prevent evaporation.

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The Role of LeavesWithin the epidermis, there are specialised cells called guard cells that control both the exchange of gases and the loss of water.

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The Role of LeavesThe cells that occur in the middle layers (mesophyll) are responsible for most of the plants photosynthesis. There are two main types of cells found in this section:Palisade Cells: elongated cells that contain numerous chloroplasts found immediately below the upper epidermisSpongy cells: contain large air spaces and their main function is gaseous exchange. They are situated in the lower leaf.

The Role of LeavesVascular tissue is distributed throughout the leaf which ensures that no cells are to far away from a source of transport.plantali.blogspot.com

The Role of Leaves

HomeworkStudents to complete:-Student Activity Table CD3.1 Comparing tissues in leaves (Bio in Focus Teacher Resource CD)

**Reminder to hand out 2.2.1 Plant Parts Handout