Answers for lab discussions!


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functions of xylem and phloem cells + more

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Answers for lab discussions!

  1. 1. Types of Reducing Sugars All monosaccharides (simple sugars that cant be broken down into smaller molecules) are reducing sugars. Two of three types of disaccharides (sugars with two chemical rings), maltose and lactose, have the open chemical structure needed to act as reducing agents. The simple structure of monosacchrides allows them to be broken down twice as quickly as disaccharides, while disaccharides must be broken into their smaller parts first.Types of Non-Reducing Sugar The third type of disaccharides, sucrose, and polysaccharides (sugars with multiple chemical rings) are non-reducing sugars. Polysaccharides--starches--have closed structures, which use free atoms to bond together their multiple rings, and take a much longer time to be broken down. Compare the function and structure of starch and lipids.Lipids are composed of glycerol and fatty acids .Starches are composed ofmonosaccharides.Carbohydrates and lipids can both be used as energy storage however carbohydrates areusually used for short term storage whereas lipids are used for long term storage. Due tolipids having less number of oxygen than in carbohydrates a lipid gives you twice as muchenergy as a carbohydrate Carbohydrates are soluble in water unlike lipids. This makescarbohydrates easy to transport around the body (from and to the store). Also,carbohydrates are a lot easier and more rapidly digested so their energy is useful if thebody requires energy fast. As for lipids, they are insoluble which makes them more difficultto transport however because they are insoluble, lipids do not have an effect on osmosiswhich prevents problems within the cells in the body. They also contain more energy pergram than carbohydrates which make lipids a lighter store compared to a store ofcarbohydrates equivalent in energy. Lipids constitute the bilayer, which is not the casewith starch.Palisade cells FunctionNucleus- control center of cell. Stores gentic informationCell wall- Protects cell and keeps it rigid.Cell membrane- Allows things to enter and exit the cell.Vacuole- Bag of liquid that keeps cells shape.Cytoplasm- Jelly-like substance which things dissolve in.Chloroplast- A green substance that collects sunlight for photosynthesis
  2. 2. These are the things that plants need for photosynthesis: carbon dioxide water Light glucose oxygenWe can show photosynthesis as this word equation: carbon dioxide + water (+ light energy) -->glucose + oxygen (Light energy is shown in brackets because it is not a substance.)This is the symbol equation for photosynthesis:Where does this process take place in the plant?Photosynthesis takes place in the chloroplasts in plant cells. Chloroplasts contain a greensubstance called chlorophyll. This absorbs the light energy needed to make photosynthesishappen. Plants can only photosynthesise in the light.
  3. 3. Palisade cells in leaves have lots of chloroplastsPlants get carbon dioxide from the air through their leaves, and water from the ground throughtheir roots.Light energy comes from the sun.The glucose produced can be turned into other substances, such as starch, which is used forstorage. The oxygen produced is released into the air from the leaves.Demonstrating photosynthesisAnimals eat to get food, but green plants make their own food. The process plants use is calledphotosynthesis. We say that plants can photosynthesise.These are the things that plants need for photosynthesis: carbon dioxide water lightThese are the things that plants make because of photosynthesis: glucose oxygenWe can show photosynthesis as this word equation:carbon dioxide + water (+ light energy) --> glucose + oxygen(Light energy is shown in brackets because it is not a substance.)
  4. 4. Where does this process take place in the plant?Photosynthesis takes place in the chloroplasts in plant cells. Chloroplasts contain a greensubstance called chlorophyll. This absorbs the light energy needed to make photosynthesishappen. Plants can only photosynthesise in the light.Palisade cells in leaves have lots of chloroplastsPlants get carbon dioxide from the air through their leaves, and water from the ground throughtheir roots.Light energy comes from the sun.The glucose produced can be turned into other substances, such as starch, which is used forstorage. The oxygen produced is released into the air from the leaves.Palisade cells are cells found within the mesophyll in leaves of dicotyledonous plants. Palisade cells havea lot of extra chloroplasts to help with photosynthesis, they are mostly found in the top surfaces of theleaves. They contain chloroplasts, which convert the energy in light to chemical energy throughphotosynthesis. The cylindrical shape of palisade cells allows a large amount of light to be absorbed bythe chloroplasts. Beneath the palisade mesophyll are the spongy mesophyll cells, irregularly-shaped cellsthat having many intercellular spaces to allow the passage of gases, such as the intake of carbon dioxidefor photosynthesis to take place. The stomata is the way in which these gases are exchanged, as well asthe transpiration of water from the xylem, either by the apoplast or symplast pathway. Palisade cells arepositioned towards the upper surface of the leaf and contain the largest number of chloroplasts per cellin plants. This makes them the primary site of photosynthesis in a plants leaves. They have a very largesurface area in order for them to absorb more light during photosynthesis.This makes photosynthesiseasier and more chemical energy can be produced for the plant. Palisade cells are found in leaves, they
  5. 5. make plants yellow. palisade cell use the light energy to turn carbon dioxide and water into glucose andoxygenFUNCTIONSCuticle-The cuticle is a waxy layer covering plants. its function is to lessen water loss by not letting itdiffuse out so easily.Plant cuticles are a protective waxy covering produced only by the epidermal cells [1] of leaves, youngshoots and all other aerial plant organs without periderm. The cuticle tends to be thicker on the top of theleaf, but is not always thicker in xerophytic plants living in dry climates than in mesophytic plants fromwetter climates, despite a persistent myth to that effect. In addition to its function as a permeability barrierfor water and other molecules, the micro and nano-structure of the cuticle confer specialised surfaceproperties that prevent contamination of plant tissues with external water, dirt and microorganisms. Manyplants, such as the leaves of the sacred lotus (Nelumbo nucifera) exhibit ultra-hydrophobic and self-cleaning properties that have been described by Barthlott and Neinhuis (1997).[8] The lotus effect haspotential uses in biomimetic technical materials."The waxy sheet of cuticle also functions in defense, forming a physical barrier that resists penetration byvirus particles, bacterial cells, and the spores or growing filaments of fungiEpidermisThe epidermis is the outer layer of cells covering the leaf. It forms the boundary separating the plantsinner cells from the external world. The epidermis serves several functions: protection against water lossby way of transpiration, regulation of gas exchange, secretion of metabolic compounds, and (in somespecies) absorption of water. Most leaves show dorsoventral anatomy: The upper (adaxial) and lower(abaxial) surfaces have somewhat different construction and may serve different functions.The epidermis is usually transparent (epidermal cells lack chloroplasts) and coated on the outer side witha waxy cuticle that prevents water loss. The cuticle is in some cases thinner on the lower epidermis thanon the upper epidermis, and is generally thicker on leaves from dry climates as compared with those fromwet climates.The epidermis tissue includes several differentiated cell types: epidermal cells, epidermal hair cells(trichomes) cells in the stomate complex; guard cells and subsidiary cells. The epidermal cells are themost numerous, largest, and least specialized and form the majority of the epidermis. These are typicallymore elongated in the leaves of monocots than in those of dicots.The epidermis is covered with pores called stomata, part of a stoma complex consisting of a poresurrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lackchloroplasts. Opening and closing of the stoma complex regulates the exchange of gases and water vaporbetween the outside air and the interior of the leaf and plays an important role in allowing photosynthesiswithout letting the leaf dry out. In a typical leaf, the stomata are more numerous over the abaxial (lower)epidermis than the adaxial (upper) epidermis and more numerous in plants from cooler climatesThe upper epidermis is responsible for preventing water loss by evaporation. It does this by having awaxy cuticle on the top of the leaf.The lower epidermis has stomata, which allow gases to enter and leave the leaf as a result ofphotosynthesis and respiration.
  6. 6. MesophyllMost of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (groundtissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation tissue isthe primary location of photosynthesis in the plant. The products of photosynthesis are called"assimilates".In ferns and most flowering plants, the mesophyll is divided into two layers: An upper palisade layer of tightly packed, vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distribution. In order to adapt to their different environment (such as sun or shade), plants had to adapt this structure to obtain optimal result. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil are single-layered. Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more rounded and not so tightly packed. There are large intercellular air spaces. These cells contain fewer chloroplasts than those of the palisade layer. The pores or stomata of the epidermis open into substomatal chambers, which are connected to the air spaces between the spongy layer cells.These two distinct layers of the mesophyll are absent in many aquatic and marsh plants. Even anepidermis and a mesophyll may be lacking. Instead, for their gaseous exchanges they use a homogeneousaerenchyma (thin-walled cells separated by large gas-filled spaces). Their stomata are situated at theupper surface.Leaves are normally green, due to chlorophyll in plastids in the chlorenchyma cells. Plants that lackchlorophyll cannot photosynthesizeChloroplastsChloroplasts are tiny, round, green food factories within the leaves of a plant. Duringphotosynthesis, they use energy from sunlight to turn chemicals in air and water into plant foodChloroplasts are those subunit in a plant cell, which produce food for a plant through theprocess of photosynthesis. Chloroplasts are somewhat similar to mitochondria found inanimal cells which can produce energy. They reproduce by the process of division of cellsand have their own genetic systems. Its the chloroplasts which convert carbon dioxide intocarbohydrates, which are consumed by plants. Moreover amino acids, lipid components andfatty acids of the cell membranes are synthesized by chloroplasts. In addition to that, theyreduce nitrogen into ammonia and other organic compounds. Once you have got the basicidea, lets take a look at how they function in a plant cell.
  7. 7. Chloroplast Function in a Plant CellChloroplast contain an important component called chlorophyll, which is responsible forproduction of food. Its the chlorophyll which gives the chloroplast and in turn, leaves itscharacteristic green color. Chlorophyll contained in the chloroplasts is responsible forabsorbing sunlight. Its through the process of photosynthesis that a plant makes food foritself. The process includes absorbing the energy from the sun so as to create sugar. Whensunlight hits a chloroplast, the chlorophyll in it uses the energy and in combination withcarbon dioxide and water forms sugar and oxygen. Plants use these sugars for survival andthe oxygen released is used by animals to breathe.Read more at Buzzle: are organelles found in plant cells and other eukaryotic organisms that conductphotosynthesis. Chloroplasts capture light energy, store it in the energy storage molecules ATP andNADPH and use it in the process called photosynthesis to make organic molecules and free oxygen fromcarbon dioxide and water.[1]Chloroplasts are green because they contain the chlorophyll pigment.(1) Absorption of light energy and conversion of it into biological energy.(2) Production of NAPDH2 and evolution of oxygen through the process of photosys ofwater.(3) Production of ATP by photophosphorylation. NADPH2 and ATP are the assimilatorypowers of photosynthesis. Transfer of CO2 obtained from the air to 5 carbon sugar in thestream during dark reaction.(4) Breaking of 6-carbon atom compound into two molecules of phosphoglyceric acid by theutilization of assimilatory powers.(5) Conversion of PGA into different sugars and store as stratch. The chloroplast is veryimportant as it is the cooking place for all the green plants. All heterotrophs also depend onplasts for this food.Phloem and xylem are complex tissues that perform transportation of food and water in a plant.They are the vascular tissues of the plant and together form vascular bundles. They worktogether as a unit to bring about effective transportation of food, nutrients, minerals and water.VASCULAR BUNDLE Xylem: tubes that bring water and minerals from the roots into the leaf. Phloem: tubes that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf.
  8. 8. The xylem typically lies on the adaxial side of the vascular bundle and the phloem typically lies on theabaxial side. Both are embedded in a dense parenchyma tissue, called the pith or sheath, which usuallyincludes some structural collenchyma tissue.Phloem XylemFunction: Transportation of food and Water and mineral transport nutrients from leaves to from roots to aerial parts of storage organs and growing the plant. parts of plant.Xylemis formed of thick-walled,tubular and often dead cells.The cells are placed end to end likedrain pipes ,and the partitions between the cell dissolve to form long pipelines for the transportof water and minerals.Xylem cells transport water and minerals absorbed by the roots from the soil. They transportthem to leaves where glucose is prepared during photosynthesis.Old Xylem forms wood and does not participate in transport.Phloem - a protective layer made up of tiny tubes that transport the sugars from the leaves to the restof the tree. Phloem carries organic nutrients to all parts of the plant where required. Its mainlyconcerned with transport of soluble organic material.Bundle-sheath cells are photosynthetic cells arranged into tightly packed sheaths around the veins of aleaf. They form a protective covering on leaf veins, and consist of one or more cell layers, usuallyparenchyma. Loosely arranged mesophyll cells lie between the bundle sheath and the leaf surface. TheCalvin cycle is confined to the chloroplasts of these bundle sheath cells in C4 plants.Cambium- It is responsible for secondary growth. It produces new phloem towards the outside of theplant and new xylem towards the inside. There are also two kinds of cells, ray initials and fusiforminitials, fusiform initials produce the xylem and phloem. Ray initials produce parenchyma cells that formrays across the stem and are used in transport between the xylem and phloem. The vascular cambium isalso responsible for producing wood.
  9. 9. In plants, the substomatal cavity is the cavity located immediately proximal to the stoma. It acts as adiffusion chamber connected with intercellular air spaces and allows rapid diffusion of carbon dioxideand other gases (such as plant pheromones) in and out of plant cells.Guard Cells- The function of the guard cells are that they help to regulate the rate of transpiration byopening and closing the stomata thus preventing excessive water loss.The function of the guard cells is that they help to regulate the rate of transpiration by opening andclosing the stomata. The guard cell opens when there is too much water. It is also adapted for gasexchange between plants and environment.For example, it opens during rainy days and closes when the weather is too dry or windy.They also control the size of the pore.Use of Guard Cells The walls surrounding the stoma are very flexible and thin; however, the opposite walls of stoma are rigid and thicker. Whenever the guard cells are inflated with internal water pressure, there is a difference in thickness in surrounding walls which results in the development of an opening. On a hot day, when the guard cells lose water, they deflate and start pushing toward each other, thus resulting in the closure of the stoma.Stoma- In botany, a pore (tiny hole) in the epidermis (outer layer of tissue) of a plant. There are lots ofthese holes, usually in the lower surface of the leaf. A leaf contains several layers of tissue. The outerlayer is the epidermis and is only one cell thick. Stomata occur in the lower epidermis.Each stoma is surrounded by a pair of guard cells that are crescent-shaped when the stoma is open butcan collapse to an oval shape, thus closing off the opening between them. Stomata allow the exchangeof carbon dioxide and oxygen (needed for photosynthesis and respiration) between the internal tissuesof the plant and the outside atmosphere.They are also the main route by which water is lost from the plant (water vapour), and they can beclosed to conserve water, the movements being controlled by changes in turgidity of the guard cells.At night the stomata may allow oxygen to diffuse in and carbon dioxide out because only respiration istaking place. Photosynthesis (photo = light and synthesis = to make) is the process plants use tochange carbon dioxide and water into sugar using sunlight. This sugar, glucose, is their food, andthe process gives off oxygen.
  10. 10. Photosynthesis is the conversion of light energy into chemical energy by living organisms. Theraw materials are carbon dioxide and water. The energy source is sunlight, and the end-productsinclude glucose and oxygen. It is arguably the most important biochemical pathway, since nearlyall life depends on it. It is a complex process occurring in higher plants, phytoplankton, algae, aswell as bacteria such as cyanobacteria. Photosynthetic organisms are also referred to asautotrophs.Photosynthesis is the process by which plants, some bacteria, and some protistans use the energyfrom sunlight to produce sugar, which cellular respiration converts into ATP, the "fuel" used byall living things. The conversion of unusable sunlight energy into usable chemical energy isassociated with the actions of the green pigment chlorophyll. Most of the time, thephotosynthetic process uses water and releases the oxygen that we absolutely must have to stayalive.We can write the overall reaction of this process as: 6H2O + 6CO2 + light → C6H12O6+ 6O26 water molecules + 6 carbon dioxide molecules + light is converted into 1 glucose molecule and 6 oxygen molecules NaHCO3 supplies dissolved CO2 to the water plant ( = aquatic plant).The immersion water is enriched by sodium hydrogen carbonate, which releases carbon dioxideto increase the rate of photosynthesis
  11. 11. Three factors can limit the speed of photosynthesis - light intensity, carbon dioxideconcentration and temperature.Light intensityWithout enough light, a plant cannot photosynthesise very quickly, even if there is plenty ofwater and carbon dioxide. Increasing the light intensity will boost the speed ofphotosynthesis. OR The relationship between light intensity and photosynthetic rate is that if theintensity of the light is high then the rate of photosynthesis will increase. However the rate ofphotosynthesis will only increase to an extent after intensity of light reaches a certain pointphotosynthesis rate will stay still.
  12. 12. I predict that the more intense the light, the higher the rate ofphotosynthesis. Plants need light. Light provides theenergy for photosynthesis to occur. Chlorophyll is an enzyme and itspeeds up the reaction. If a plant does not get enough of either ofthese things, photosynthesis will not happen as quickly, if at all.Therefore, I predict that when the light is not very intense we willnot see so many bubbles being produced. This is because the plant willnot have so much energy (derived from light) to activatephotosynthesis. All reactions require certain activation energy, andif this is not reached the reaction will occur more slowly. I thinkthat as we move the lamp away (and therefore reduce the lightintensity) from the pondweed the number of bubbles produced willdecrease steadily. For instance, say at 10cm distance 50 bubbles arecounted, it is likely that at 20cm distance 25 bubbles will becounted, as the lamp is twice the distance away. This means the rateof photosynthesis is halved but we are measuring the light intensityand so this will not mean the rate of photosynthesis is halved. Ithink that if we move the lamp any further away than 50cm no bubblesat all will be produced because there will simply not be enough lightfor photosynthesis to work but we are only doing it till 17cm whichwill give us enough results.When I am doing my experiment I will measure the amount of oxygen madewhich will be measured by the bubbles.I will vary the distance apart from the beaker to the lamp. Theequipment I will be using are as follows: a large beaker, a healthypondweed plant, a lamp, water, a stopwatch, a pinch of sodiumbicarbonate which will give the plant more carbon dioxide.6 Suggest another way to measure the rate of photosynthesis.Record the number of oxygen bubbles given off per unit time.Record the total volume of oxygen evolved in a fixed interval of time. 9 What precautions should be taken? any oneInclude a heat shield and check its temperature at intervals.l Make sure the apparatus is air-tight by closing the clip completely.l Don’t spray water onto the hot light bulb.