Transport in Plants 2023 PDF

Transport in Plants  Overview Plants are multicellular Plants are eukaryotes Plant cells are similar to animal cells but with cell walls and a large vacuole Kingdom Plantae  Learning Objectives 1. State the three ways by which substances are moved in pl...

Transport in Plants  Overview Plants are multicellular Plants are eukaryotes Plant cells are similar to animal cells but with cell walls and a large vacuole Kingdom Plantae  Learning Objectives 1. State the three ways by which substances are moved in plants – long, apo, symplast 2. Recall the processes of diffusion, osmosis, facilitated diffusion and active transport 3. Explain the process of mineral uptake in plants 4. Different between long and short distance transport and between the apoplastic and symplastic pathways 5. Describe the movement of water from the soil to the atmosphere, through the plant (name all of the processes) 6. Define transpiration 7. State the factors which affect the rate of transpiration  Learning Objectives 1. Differentiate between the xylem and phloem based on structure and function 2. Explain how leaves, stems and roots are adapted for transport in plants Plant Cell Structure cell wall chloroplast nucleus central vacuole  How do plants get what they need? What do plants need for healthy growth? minerals water sunlight oxygen for respiration 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.  Moving materials How do plants transport materials to where they are needed?  Moving Materials (contd) Transport in Plants occurs on three (3) levels: (1) the uptake and loss of water and solutes by individual cells (2) short-distance transport of substances from cell to cell at the level of tissues or organs (3) long-distance transport of sap within xylem and phloem at the level of the whole plant. CELL TRANSPORT PROCESSES  Cell Transport Processes Cell membrane is selectively permeable. – Passive Transport: - Simple Diffusion - Osmosis - Facilitated diffusion (transport proteins) – Active Transport: need ATP energy Simple Diffusion  Osmosis Osmosis Water Relations of Plant Cells Facilitated Diffusion  Passive Versus Active Transport Passive Versus Active Transport  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. SHORT DISTANCE TRANSPORT  In most plant tissues, the cell wall and cytosol are continuous from cell to cell. The cytoplasmic continuum is called the symplast. The cytoplasm of neighboring cells is connected by channels = plasmodesmata. The apoplast is the continuum of cell walls and extracellular spaces. Short Distance Cell wall Transport Cytosol Vacuole Plasmodesma Vacuolar membrane Plasma membrane (a) Cell compartments Key Transmembrane route Apoplast Apoplast Symplast Symplast Symplastic route Apoplastic route (b) Transport routes between cells  Short-Distance Transport Involves simple diffusion, osmosis and active transport. Routes – Cell-to-Cell Across Cell Membranes – Symplast (involves cytoplasm and plasmodesmata) – Apoplast (transport through porous cell walls) Short-Distance Transport LONG DISTANCE TRANSPORT How do tall trees get enough water? Involves transpiration and root pressure Continuous tube of water depends upon water cohesion and adhesion. Long-Distance Transport  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. 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? humidity (amount of moisture in the air) light intensity temperature air movement (wind). Guard Cells Mediate Transpiration Stomatal Opening and Closing Stomatal Opening and Closing TRANSPORT TISSUES IN PLANTS  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. Vascular Bundles  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.  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. 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.  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.  How are leaves adapted for diffusion? The diffusion of gases occurs in the leaves. They are adapted for this function in the following ways: Leaves are thin. This decreases the distance gases have to travel between the air and cells. There are air spaces between cells. This increases the speed of diffusion from the air to the cells inside the leaf. There are lots of stomata (pores) on the undersides of leaves. These let gases in and out.  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? How are plant stems adapted for transport? – Vascular bundles: these are made up of xylem vessels and phloem sieve tubes These specialized tissues reach from the bottom of the roots, through the stems to the tips of leaves  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? high surface area to volume ratio maximum contact with the soil firm anchorage.