★Unit-4_ Food Making and Growth in Plants (1) (2).pdf

FOOD MAKING AND GROWTH IN PLANTS 2023 UNIT FOUR FOOD MAKING AND GROWTH IN PLANTS 4.1. THE LEAF  The most numerous parts on most plants are their leaves. Leaves are considered...

FOOD MAKING AND GROWTH IN PLANTS 2023 UNIT FOUR FOOD MAKING AND GROWTH IN PLANTS 4.1. THE LEAF  The most numerous parts on most plants are their leaves. Leaves are considered to be a plant organ. An organ is a group of tissues that performs a specialized task.  Leaf, in botany, any usually flattened green outgrowth from the stem of a vascular plant.  As the primary sites of photosynthesis, leaves manufacture food for plants, which in turn ultimately nourish and sustain all land animals.  Botanically, leaves are an integral part of the stem system, and they are initiated in the apical bud (growing tip of a stem) along with the tissues of the stem itself.  Certain organs that are superficially very different from the usual green leaf are formed in the same manner and are actually modified leaves; among these are the sharp spines of cacti, the needles of pines and other conifers, and the scales of an asparagus stalk or a lily bulb. Figure: The leaves Nazareth School/ Grade 10 Tesfalem T. Page 1  FOOD MAKING AND GROWTH IN PLANTS 2023 Adaptations of a leaf for photosynthesis  Most of the leaves are flat and wide (this gives a large surface area to collect light and short distances for gases to diffuse).  The main function of a leaf is to produce food for the plant by photosynthesis. Chlorophyll, the substance that gives plants their characteristic green color, absorbs light energy. 1. External structure of a leaf  Typically, a leaf consists of a broad expanded blade (the lamina), attached to the plant stem by a stalk like petiole. Leaves are, however, quite diverse in size, shape, and various other characteristics, including the nature of the blade margin and the type of venation (arrangement of veins). Figure: External structure of a leaf  Blade (Lamina) – is the broad flat part of the leaf.  Mid-rib – is the main vein which support the lamina and transport materials to and from the leaf tissues, radiate through the lamina from the petiole.  Apex – the tip and narrower region of the leaf.  Margin – is the leaf border. Nazareth School/ Grade 10 Tesfalem T. Page 2  FOOD MAKING AND GROWTH IN PLANTS 2023  Plant leaves come in all sizes and shapes.  The leaf may be simple—with a single blade—or compound—with separate leaflets; it may also be reduced to a spine or scale. Figure: Common leaf morphologies. 2. Internal structure of a leaf  Although a leaf looks thin, it is in fact made up of several layers of cells.  When we see the transverse section of a leaf under a microscope, we observe three distinct types of tissues. These are:- A. Epidermis B. Mesophyll C. Vascular tissue (veins) Nazareth School/ Grade 10 Tesfalem T. Page 3  FOOD MAKING AND GROWTH IN PLANTS 2023 Figure: This cross section of a leaf shows that leaves of plants are perfectly adapted to make the best possible use of the light that falls on them. Nazareth School/ Grade 10 Tesfalem T. Page 4  FOOD MAKING AND GROWTH IN PLANTS 2023 A. Epidermis  The upper and lower surface of the leaf.  The upper layer is covered by a waxy cuticle.  Waxy cuticle serves as a water proof (it prevents the loss of water).  In the lower layer there is a small opening known as stomata.  It is in the stomata where gas exchange and transpiration takes place.  The opening and closing of the stomata is controlled by guard cells. B. Mesophyll tissue  It is found next to the epidermis.  It has two distinct regions, i.e. i. Palisade Mesophyll  These cells contain numerous chloroplasts; as a result, it is the main site for the process of photosynthesis. ii. Spongy Mesophyll  Some photosynthesis takes place here but it concerns more in the exchange of gases and transpiration because it contains lots of air spaces. C. Vascular bundles  Contains xylem and phloem tissue.  Xylem tissue – is a dead tissue which is responsible for the transport of water and minerals.  Phloem tissue – is a living tissue which is responsible for the transport of organic food. Nazareth School/ Grade 10 Tesfalem T. Page 5  FOOD MAKING AND GROWTH IN PLANTS 2023 4.2. PHOTOSYNTHESIS  ALL living organisms need energy to grow, move and reproduce.  Based on their feeding habit we can classify organisms in to two : o Autotrophs /also called Producers/  Those organisms that can make their own foods.  Examples; Plants and Algae. o Heterotrophs / also called Consumers/  Those organisms that cannot make their own foods and directly or indirectly depend on autotrophs.  Examples: Animals Q. What is photosynthesis?  The word photosynthesis can be separated to make two smaller words:  “Photo” which means light.  “synthesis” which means putting together.  Plants need food but they do not have to wait on people or animals to provide for them. Most plants are able to make their own food whenever they need it. This is done using light and the process is called photosynthesis.  The process of making food of autotrophic organisms by capturing solar energy and using it to convert carbon dioxide and water into simple sugars is called photosynthesis.  The process of converting light energy (kinetic) into energy stored in the covalent bonds of glucose molecules (potential).  Carried out by photoautotrophs:  Plants, phytoplankton, cyanobacteria (any photosynthetic organism).  The basis of almost all ecosystems  all “food energy” ultimately comes from the sun.  source of all atmospheric oxygen (O2) Q. What is needed for Photosynthesis?  To make food, plants need not just one but all of the following:  Chlorophyll – the light absorbing green pigment found in the chloroplast.  Water – from the soil that is absorbed by the roots and passes through vessels in the stem on its way to the leaves. Nazareth School/ Grade 10 Tesfalem T. Page 6  FOOD MAKING AND GROWTH IN PLANTS 2023  Carbon dioxide - from the air passes through small pores (holes) in the leaves. These pores are called stomata.  Light – from the sun that is absorbed by a green chemical in the leaves.  The immediate products of photosynthesis are glucose and oxygen.  Some of the glucose is used to provide energy for the growth and development of plants while the rest is converted to the large polysaccharide molecules called starch and stored in leaves, roots or fruits for later use by plants.  Enzyme regulates the whole process of photosynthesis. Photosynthesis can be summed up in the following equation: Figure: The overall process of photosynthesis. Nazareth School/ Grade 10 Tesfalem T. Page 7  FOOD MAKING AND GROWTH IN PLANTS 2023  Some of the glucose produced during photosynthesis is used immediately by the cells of the plant for respiration to provide energy for cell functions, growth and reproduction.  The energy released in respiration is used to build up smaller molecules into bigger molecules:  Sugars like glucose are built into starch for storage.  Sugars like glucose are built into molecules like fructose (fruit sugar) and sucrose (a double sugar unit) to be transported around the plant.  Sugars like glucose are built up into more complex carbohydrates like cellulose to make new plant cell walls.  Sugars, along with nitrates and other nutrients that the plant takes up from the soil, are used to make amino acids. These amino acids are then built up into proteins to act as enzymes and make up much of the cytoplasm of the cells.  Sugars may be built up into fats and oils (lipids) for storage in seeds and to make up part of the cell membranes.  Sugars may be used to build up important large molecules such as chlorophyll, using minerals such as magnesium taken up from the soil. Nazareth School/ Grade 10 Tesfalem T. Page 8  FOOD MAKING AND GROWTH IN PLANTS 2023 THE PROCESS OF PHOTOSYNTHESIS Q. What happens during Photosynthesis?  The photosynthesis process takes place in the leaves of plants. The leaves are made up of very small cells. Inside these cells are tiny structures called chloroplasts.  Each chloroplast contains a green chemical called chlorophyll which gives leaves their green color. Figure: The structure of Chloroplast  Chlorophyll absorbs the sun’s energy.  It is this energy that is used to split water molecules into hydrogen and oxygen.  Oxygen is released from the leaves into the atmosphere.  Hydrogen and carbon dioxide are used to form glucose or food for plants.  Here is the process in greater detail:  In order to make food, the process should pass two stages, i.e.:- 1. Light- dependent stage (Light reaction) 2. Light-independent stage (Dark reaction) 1. Light reaction  This is the light-dependent stage of photosynthesis.  This stage occurs in the thylakoid of chloroplast. Nazareth School/ Grade 10 Tesfalem T. Page 9  FOOD MAKING AND GROWTH IN PLANTS 2023  This stage has two main functions: I. The chlorophyll absorbs the energy of the sun light.  Therefore, some of the energy is used to split the water molecules into hydrogen and oxygen. Light - 12H2O 6O2 + 24H+ + 24e Chlorophyll II. The rest of the energy forms the energy-rich compound, i.e. ATP and NADPH,  It is the electrons and hydrogen ions that are used to create ATP and NADPH.  ATP is an energy storage molecule.  NADPH is an electron carrier/donor molecule, which is formed when hydrogen combines with the co-enzyme NADP, which acts as hydrogen carrier to form NADPH.  Both ATP and NADPH will be used in the next stage of photosynthesis, i.e. in dark reaction for the synthesis of glucose. 2. Dark reaction  This is the light-independent stage of photosynthesis.  The reaction occurs in the stroma of chloroplasts. Nazareth School/ Grade 10 Tesfalem T. Page 10  FOOD MAKING AND GROWTH IN PLANTS 2023  The dark reaction does not have to occur in the dark, but they simply do not require light.  Although these reactions can take place without light, the process requires ATP and NADPH which were created using light in the first stage.  Carbon dioxide and energy from ATP along with NADPH are used to form glucose. So, its function is to make glucose.  During this reaction, CO2 and hydrogen are combined to form glucose. 6CO2 + 24H+ C6H12O6 + 6H2O The net reaction is summarized as:- Light 12H2O 24H+ + 6O2 (Light rxn) Chlorophyll 6CO2 + 24H+ C6H12O6 + 6H2O (Dark rxn) Light 6H2O + 6CO2 Chlorophyll C6H12O6 + 6O2 (Net rxn) Figure: The light-dependent and –independent reaction of photosynthesis Nazareth School/ Grade 10 Tesfalem T. Page 11  FOOD MAKING AND GROWTH IN PLANTS 2023 Dark rxn DARK occur in the REACTIONS liquid stroma Light rxn occur in the thylakoid Figure: Summary of photosynthesis. The need for light  Light is needed for splitting water into hydrogen and oxygen.  Splitting of water molecules using light is called photolysis.  To demonstrate sunlight is essential for photosynthesis:  Destarching a plant by putting it in darkness for few days, it loses its starch, this process is called destarching. (Destarching the process of eliminating starch reserves from a plant by depriving it of light).  Then test the leaf for starch in iodine solution.  Result: No blue-black (negative result) shows that the absence of starch. Nazareth School/ Grade 10 Tesfalem T. Page 12  FOOD MAKING AND GROWTH IN PLANTS 2023 Figure: The results of the iodine test for starch: leaf A is from a destarched plant which has been kept in the dark; leaf B is from a plant kept in the light. The need for carbon dioxide  A source of carbon is needed for the plants to synthesize sugars.  There are lots of carbon-containing chemicals in existence, but carbon dioxide from the air or in solution in water is the only form that plants can use in photosynthesis.  To demonstrate that plants need CO2 for photosynthesis:  Put the plant in a bell jar which does not allow air to enter, and place potassium hydroxide solution.  Potassium hydroxide has an ability to absorb CO2 from surrounding air.  Place in light for few hours.  Test leaf for starch.  Result: The plant produces less starch; this is because the KOH absorbs the CO2 which made the plant to face shortage of CO2 to make enough starch. This graph shows the direct relationship between CO2 and starch production, i.e. if the level of CO2 increases starch production will also increases. Nazareth School/ Grade 10 Tesfalem T. Page 13  FOOD MAKING AND GROWTH IN PLANTS 2023 The need for chlorophyll  Chlorophyll is needed to absorb sunlight, which is used as a main source of energy for the process of photosynthesis.  To demonstrate the need of chlorophyll for photosynthesis:  Test a variegated leaf for starch.  Variegated leaf is a leaf which is not completely green and has yellowish or white spot, i.e. variegated leaves have areas that contain chlorophyll and areas that do not.  Result: Only the greenish part turns blue-black. Therefore, the variegated parts which have no chlorophyll do not produce starch. This shows that without chlorophyll photosynthesis did not take place. Figure: Testing of a variegated leaf for starch. The need for water  Water is needed during photosynthesis as a source of hydrogen ion found in glucose molecule.  To demonstrate the need for water in photosynthesis:  Supply the plant with ‘heavy’ water containing the 18O isotope of oxygen.  These atoms are radioactive, and the radiation they produce can be detected as it is taken up and used by the plant. Substances like this are known as radioactive tracers.  The experiment shows that oxygen gas produced during photosynthesis comes from the splitting of the water molecules using light energy. Nazareth School/ Grade 10 Tesfalem T. Page 14  FOOD MAKING AND GROWTH IN PLANTS 2023 The importance of photosynthesis Q. What does Photosynthesis produce?  Photosynthesis is one of the most important reactions on Earth.  It is through photosynthesis that the ultimate source of energy for the Earth – in other words, the sun – is trapped and converted into chemical energy which is available to life.  Photosynthesis provides two main things:  Food  Oxygen  Photosynthesis is very important as the source of energy for almost all living organisms, because of the way in which photosynthesis provides us with new biological material.  Photosynthesis is so essential to life on earth that most living organisms, including humans, cannot survive without it.  Some of the glucose that plants produce during photosynthesis is stored in fruits and roots. This is why we are able to eat carrots, potatoes, apples, water melons and all the others. These foods provide energy for humans and animals.  All of our energy for growth, development and physical activity comes from eating food from plants and animals. Animals obtain energy from eating plants. Plants obtain energy from glucose made during photosynthesis.  Almost all living organisms need oxygen for cellular respiration.  That oxygen is produced as a waste product of photosynthesis.  We need enormous numbers of plants to photosynthesize to maintain atmospheric and water oxygen levels.  Other importance of photosynthesis:  Our major sources of energy such as natural gas, coal and oil were made millions of years ago from the remains of dead plants and animals which we already know got their energy from photosynthesis.  Photosynthesis is also responsible for balancing oxygen and carbon dioxide levels in the atmosphere. Nazareth School/ Grade 10 Tesfalem T. Page 15  FOOD MAKING AND GROWTH IN PLANTS 2023 4.3. Transport A double transport system  Plants need an adequate supply of water, oxygen, carbon dioxide and mineral elements in order to satisfy their requirements for metabolism and growth. These materials together with the products of photosynthesis are transported through the entire body of the plant.  This takes place in specialized conducting vessels which are located in groups known as vascular bundles.  Lower plants like mosses have no special transport system, so movement of food materials and other substances can take place by diffusion, osmosis and active transport, and does not require specialized conducting tissues.  In higher plants gases move by diffusion, while transportation of water, mineral and food takes place through specialized tissues called vascular bundles (xylem and phloem).  Therefore, transportation in plants is known to be a double transport system. It requires two separate transport system: xylem and phloem.  Xylem tissue  Principal water conducting tissue.  Consists of hollow, dead cells.  The movement of the water in the xylem is due to transpiration, and it is passive. This means it uses no energy from the plant.  Water conducted in an unbroken stream from roots to leaves.  Also provides mechanical support for plant body. Nazareth School/ Grade 10 Tesfalem T. Page 16  FOOD MAKING AND GROWTH IN PLANTS 2023  Types and arrangement of xylem cells used to identify many species of plants.  Phloem tissue  Located toward outer part of roots and stems.  Principal food conducting tissue.  Transportation of food or organic substances from the leaf to parts of a plant is called translocation.  The plant has to use energy to move substances around the phloem, and food substances can move both up and down the plant.  The vascular tissues in plants are differently arranged in the root, the stem and veins in leaves.  The pattern of organization of these tissues also depends on which of the two major groups of flowering plants the plant belongs, i.e. dicots and monocots.  The arrangement of the bundles in the monocot stem is markedly different from that in the dicot stem. Figure: The transport system in a non-woody plant is arranged in bundles around the outside of the stem, with the xylem and the phloem arranged together. In the root the transport tissue is all in the center. Nazareth School/ Grade 10 Tesfalem T. Page 17  FOOD MAKING AND GROWTH IN PLANTS 2023 How does water enter the plant body?  Water is essential for all physiological activities of the plant and plays a very important role in all living organisms.  We know that the roots absorb most of the water that goes into plants.  The responsibility of absorption of water and minerals is more specifically the function of the root hairs that are present in millions at the tips of the roots.  Root hairs are thin-walled slender extensions of root epidermal cells that greatly increase the surface area for absorption; this also increases absorption of water and mineral ions. Figure: The cross-section of root cell.  Here is the mechanism of absorption of water by root hairs:  The cell sap of the root hair is relatively more concentrated than the water that surrounds the root hairs.  Because of this concentration difference, water passes from the soil via the cell wall and the thin cytoplasmic lining in to the vacuole of the root hairs by a process known as osmosis.  Once the water enters the vacuole of the root hairs, the extra water dilute the cell sap. This creates a potential difference to that of the next cell (adjacent cell).  This rise in the osmotic potential and turgor pressure in the cell.  The difference in the water content and the turgor pressure in the cells forces water to enter into the adjacent cells. In the same way, water passes into the next cell until it enters the water vessels of the xylem. Nazareth School/ Grade 10 Tesfalem T. Page 18  FOOD MAKING AND GROWTH IN PLANTS 2023 Figure: Water moves across the tissues of a plant by osmosis. It moves along a water potential gradient. The transpiration stream Q. How does water travel within the plant body?  The transport of water through a plant is the result of the transpiration stream.  Transpiration – is the process by which the plant loses water as water vapors from the surface of the leaves into the atmosphere. It occurs mainly through the stomata in the leaves.  Here is the mechanism of water travel within the plant body: During transpiration the concentration of water molecules in the cells of the leaves decrease. This leads the leaves under tension, the tension develops pulling force. As a result these cells withdraw water from the nearby adjacent cells or xylem vessels of the veins. These pulling force continue to the root hair trough steam. The root in turn absorbs water from the soil to replace the water which flows into the stem.  This is called transpiration stream (pull). Nazareth School/ Grade 10 Tesfalem T. Page 19  FOOD MAKING AND GROWTH IN PLANTS 2023 Figure: The transpiration stream – capable of pulling a column of water in the xylem up to 30 m above the surface of the Earth.  Therefore, transpiration stream is the main force responsible for the water passing up all the way from the roots to the leaves.  It is associated by mechanisms like cohesion, adhesion, root pressure (hydrostatic pressure) and capillarity of water. 1. Cohesive force  It is a strong force of attraction between water molecules.  Water molecules stick together in order to move along xylem vessels. As a water molecule evaporates from the surface of the leaf, it pulls on the adjacent water molecule, creating a continuous flow of water through the plant. Figure: Water movement due to cohesion Nazareth School/ Grade 10 Tesfalem T. Page 20  FOOD MAKING AND GROWTH IN PLANTS 2023 2. Adhesive force  It is a force of attraction between water molecules and the xylem vessels. Figure: Movement of water in xylem 3. Root pressure  It is the pressure created in the root as a result of turgidity of the root cells when water enters into them from the soil.  It moves the water a short distance, i.e. less than a meter. 4. Capillarity  It is the ability of water to rise in fine (narrow) tubes.  Since the xylem vessels are made from narrow tubes they serve as capillary tube.  Water can move upward for a short distance due to capillarity. Nazareth School/ Grade 10 Tesfalem T. Page 21  FOOD MAKING AND GROWTH IN PLANTS 2023 Overview of transpiration: 1. Water is passively transported into the roots and then into the xylem. 2. The forces of cohesion and adhesion cause the water molecules to form a column in the xylem. 3. Water moves from the xylem into the mesophyll cells, evaporates from their surfaces and leaves the plant by diffusion through the stomata. Figure: Transpiration stream Evaporation from the leaf sets up a pressure gradient between the outside air and the air spaces of the leaf. The gradient is transmitted into the photosynthetic cells and on the water- filled xylem in the leaf vein. Figure: Water movement in the leaf. Nazareth School/ Grade 10 Tesfalem T. Page 22  FOOD MAKING AND GROWTH IN PLANTS 2023  Importance of transpiration:  Creates transpiration pull for absorption and transport of plants.  Supplies water for photosynthesis.  Transports minerals from the soil to all parts of the plant: the water that enters the root contains dissolved nutrients vital to plant growth. It is thought that transpiration enhances nutrient uptake into plants.  Cools leaf surfaces by evaporative cooling.  Maintains the shape and structure of the plants by keeping cells turgid.  Carbon dioxide entry: When a plant is transpiring, its stomata are open, allowing gas exchange between the atmosphere and the leaf. Open stomata allow water vapor to leave the leaf but also allow CO2 to enter. Active transport  Active transport involves the movement of molecules against concentration gradient.  It requires expenditure of energy from cells metabolism.  Plants need active transport during: ► Absorption of mineral ions from the soil.  Minerals are needed for making of proteins and other molecules within the cell. ► Transportation of food from the leaf to parts of a plant. Figure: It takes the use of energy in active transport to move mineral ions against a concentration gradient like this. Nazareth School/ Grade 10 Tesfalem T. Page 23  FOOD MAKING AND GROWTH IN PLANTS 2023 The need for transport in plants  To circulate water, essential nutrients, excretory products, and gases within the plants for various purposes, transportation in plants is necessary. In vascular tissues, this transportation in the plant takes place.  For the process of photosynthesis, raw materials should be transported to the leaves.  All the cells of plant needs glucose for cellular respiration as well as material for growth. The sugars that are produced in the leaves and carried all around the plant can also be stored.  Plants store glucose in the form of starch which is osmotically inactive. The starch which is stored can be converted into glucose when needed by the plant mostly when the plant is not photosynthesizing.  Plants store starch at different storage organs: roots, steams, leaves, as well as fruits and seeds.  Storage organs are important for a plant to survive difficult conditions. Nazareth School/ Grade 10 Tesfalem T. Page 24  FOOD MAKING AND GROWTH IN PLANTS 2023 Factors affecting the rate of transpiration  Because the transpiration stream is driven mainly by the evaporation of water from the leaves, anything which affects the rate of evaporation will affect transpiration.  Conditions which increase the rate of evaporation also increase the rate of transpiration.  Some of the factors that affect the rate of transpirations are: 1. Temperature  As the temperature increase the rate of transpiration increase.  The higher the temperature, the more evaporation takes place. 2. Light  Light makes stomata to stay open, which is for photosynthesis. However, when the stomata opens water evaporates from the leaf, so plenty of light speeds up transpiration. 3. Number of stomata  If a leaf has many stomata, it increases the exposure of the leaf to lose more water. Stomata 4. Air movement (wind)  Water vapor around the stomatal opening is swept away from the leaf by air movements or wind which increase the rate of water vapor to diffuse out. This maintains a good concentration gradient for diffusion and increases evaporation. Nazareth School/ Grade 10 Tesfalem T. Page 25  FOOD MAKING AND GROWTH IN PLANTS 2023 5. Humidity  When the concentration of water vapor in the atmosphere is saturated less amount of water diffuse (evaporates) into the atmosphere from the leaf.  Water evaporates more rapidly into dry air than into humid air.  So transpiration is more rapid in hot, dry and windy conditions than it is in still or humid conditions. Table: Summary of rate of transpiration under different factors Feature Effect on transpiration Number of More leaves (or other photosynthesizing organs) means a bigger surface area leaves and more stomata for gaseous exchange. This will result in greater water loss. Number of More stomata will provide more pores for transpiration. stomata Size of the A leaf with a bigger surface area will transpire faster than a leaf with a smaller leaf surface area. A waxy cuticle is relatively impermeable to water and water vapor and Presence of reduces evaporation from the plant surface except via the stomata. A plant cuticle reflective cuticle will reduce solar heating and temperature rise of the leaf, helping to reduce the rate of evaporation. These are some examples of the adaptations of plants for conservation of water that may be found on many xerophytes. The rate of transpiration is controlled by stomatal aperture, and these small Light supply pores open especially for photosynthesis. In general, a light supply will encourage open stomata. Temperature affects the rate in two ways: Temperature 1. An increased rate of evaporation due to a temperature rise will hasten the loss of water. 2. Decreased relative humidity outside the leaf will increase the water potential gradient. Relative Drier surroundings give a steeper water potential gradient, and so increase humidity the rate of transpiration. In still air, water lost due to transpiration can accumulate in the form of vapor Wind close to the leaf surface. Wind blows away much of this water vapor near the leaf surface, making the potential gradient steeper and speeding up the diffusion of water molecules into the surrounding air. Water Water stress caused by restricted water supply from the soil may result in supply stomatal closure and reduce the rates of transpiration. Nazareth School/ Grade 10 Tesfalem T. Page 26  FOOD MAKING AND GROWTH IN PLANTS 2023 Adaptations of plants to reduce water loss  Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99% of water absorbed from the soil is lost by transpiration.  If a plant begins to lose water faster than it is replaced by the roots, it runs the risk of wilting. Thus, plants need to reduce the rate of transpiration through various adaptations. Some of these are: 1. Waxy cuticle  Water proofs structure on the surface of the leaf, this structure reduces evaporation from the plant surface since it is relatively impermeable to water and water vapor. 2. Reduced number of stomata  On some plants the stomata are sunk into pits.  Less number of stomata means less transpiration rate. 3. Stomata on the underside of the leaf  This reduces exposure of the leaf to the sun. 4. Reduced number of leaves  As number of leaves decrease rate of transpiration decrease 5. Reduced size of leaves to very narrow spikes  This reduces the surface area over which water may be lost. 6. Developed very hairy leaves  Which trap a micro-atmosphere around the stomata and reduce water lose. 7. Rolled their leaves  Example grass, which is used to trapping a micro-environment of moist air inside. 8. Developed fleshy leaves /succulent leaves/  It helps to store water. Figure: Aloe vera – this plant stores water in its fleshy leaves. Nazareth School/ Grade 10 Tesfalem T. Page 27  FOOD MAKING AND GROWTH IN PLANTS 2023  The purpose of all these adaptations is to reduce the loss of water from the leaves by transpiration, so the plant can photosynthesize and avoid wilting whatever the conditions around it. Transpiration and agriculture  Transpiration has many implications for the way we grow our crops – and the crops we choose to grow. If our crop plants do not get enough water, then they will not be able to transpire and they will wilt, so farmers must work for the mechanisms that reduce water loss.  Here are some mechanisms to reduce the rate of transpiration in the fields of agriculture:  Growing plants which transpire less.  Destroying unwanted weeds.  Removing dying or damaged leaves.  Growing crops in relatively sheltered places.  Reducing air movements over the crop by planting taller plants in rows along the direction of wind break.  Choosing crops which are suited to the conditions where we are growing them. Nazareth School/ Grade 10 Tesfalem T. Page 28