Po Leung Kuk Choi Kai Yau School Name: IGCSE Biology 2017-2019 Date: B6. Animal Nutrition Plant Nutrition Syllabus Requirement: Core Supplement • Define photosynthesis • State word and symbol equations for photosynthesis • Describe the intake of raw materials, the trapping and storing of energy, the formation of food substances and their subsequent storage • demonstrate the significance of these features in terms of functions • describe the importance of nitrate ions for protein synthesis and magnesium ions for chlorophyll synthesis • describe the uses and the dangers of overuse of nitrogen fertilizers explain the effects of nitrate ion and magnesium ion deficiency on plant growth • Use hydrogencarbonate indicator solution to investigate the effect of gas exchange of an aquatic plant kept in the light and in the dark • Describe the use of carbon dioxide enrichment, optimum light and optimum temperatures in glasshouses in temperate and tropical countries • Outline the subsequent use and storage of the carbohydrates made in photosynthesis • Design and invesitigate how the limiting factors can affect the rate of photosynthesis in the water plant • Identify the cellular and tissue structure of a dicotyledonous leaf • Demonstrate the significance of these features in terms of functions • Describe the importance of nitrate ions for protein synthesis and magnesium ions for chlorophyll synthesis • Describe the uses and the dangers of overuse of nitrogen fertilizers Adopted from Cambridge IGCSE Biology 0610. Syllabus for examination in 2016, 2017 and 2018. Biology at Glance IGCSE and GCSE review, Revision Guide Oxford 1 Photosynthesis 1. Plants are autotrophs . They can use simple inorganic substances to make the organic substances they need. This mode of nutrition is called autotrophic nutrition. 2. Plants can carry out photosynthesis. In the process, carbon dioxide from the air and water from the soil are used to make food in the form of glucose using light energy trapped by the chlorophyll. Oxygen is released as a by- product. 3. In all plants, photosynthesis occurs in chloroplasts which contain chlorophyll. In most plants, this pigment is green. Chlorophyll absorb light energy to drive the photosynthetic reaction by which water is split and added to carbon dioxide and water . As a result, glucose is made and stored in the form of starch and oxygen is made as a by-product. SUMMARY: Water, carbon dioxide, chlorophyll, sun light are required for photosynthesis. Glucose is produced and stored in the chloroplast and other storage organs as starch. Oxygen is produced as a by-product and released from the leaf. 2 Site of Photosynthesis Question: 1. What is photosynthesis? 2. I what part of the plant does photosynthesis occur? 3. Why does photosynthesis take place only during the day? 4. Carbon dioxide is needed for photosynthesis. How does it enter the plant? 5. In which layer of the leaf does photosynthesis take place and why? 6. Describe three ways in which leaves are suited for photosynthesis. What are the adaptive features of the leaf Structure of the leaf Adapted for photosynthesis • Broad and flat. • Provides a large surface area for absorbing light. • thin Gasses and light can reach the photosynthetic cells easily. • Consists of tightly packed cells that contain many chloroplast. • Located on the upper side of the leaf. • Columnar in shape. • minimizes any space wastage for maximum light absorption • absorbs more sun light directly • columns of cells minimize any waste of incoming light • Consists of loosely packed cells that contain many air spaces. • allows gases to diffuse freely inside the leaf • covered by thin layer of waxy cuticle • Reduces water loss from the leaf, keeping the water in the leaf for photosynthesis and cell turgidity. • any light from the sun is passed through to the palisade mesophyll layer Leaf blade Palisade mesophyll Spongy mesophyll • does not contain chlorophyll Upper and lower epidermis Midrib • Contains numerous stomata (more on lower epidermis), each surrounded by a pair of guard cells. • guard cells open the stoma when the conditions are favorable for photosynthesis and close it when the conditions are less favorable. This allows the passage of gases and water vapor into and out of the leaf. • Contains a vascular bundle made up of xylem and phloem. • Branches into a network of veins. • provides efficient transport of materials: water into and food away form the leaf. • supports and maintains the shape of 3 Raw materials for photosynthesis Roots absorb water and minerals from the soil Cell wall cytoplasm nucleus vacuole How are root cells adapted to its function of absorption? The root cells have root hair cells that extend into the soul. This increases the surface area for more absorption of minerals and water from the soil. Cell membrane Where is the site of gas exchange for photosynthesis? nucleus chloroplast vacole vacuole cell wall Explain how the guard cells work to regulate the rate of gas exchange in and out of the leaf. water enters the guard cells guard cells swell up and become turgid pulls the guard cells apart stomata open allowing gases to diffuse water moves out of the guard cells Guard cells lose water and become flaccid the guard cells collapse together stomata closes stopping gases from diffusing CO2 goes in O2 goes out Other than gases, what is stored in the air spaces of the spongy mesophyll? Water can be stored in the spaces when there is excess water. Water can evaporate from the stomata through transpiration as water vapour. 4 Relationship between photosynthesis and respiration How is photosynthetic rate affected by different seasons? When is it highest? Winter: day light is less, temperatures are lower. Less photosynthesis takes place. Summer: day light is longer, temperatures are more. More photosynthesis takes place. What is the effect of light intensity on gas exchange? Approximately, what time of the day do A, B, C, D and E correspond to? A: midnight-early morning 7:30pm-6:30am D: morning to midday8:30am-12:30pm B: dusk, sunrise 6:30-7:00am E: 12:30am-mid afternoon C: sun rise 7:00am-8:30am 5 Relationship between photosynthesis and respiration 6 Requirements for photosynthesis How do we know that photosynthesis has occurred? 1. Glucose molecules formed in photosynthesis are quickly built into starch molecules. Therefore we can test for the presence of starch to test whether photosynthesis has occurred or not. 2. We can test for the presence of starch in leaves using iodine solution. 3. Positive test for starch shows blue-black when reacted with iodine and a negative test for starch shows brown. 4. Since oxygen is also produced, glowing splint can be used to test for oxygen. In aquatic plants, what can be used to test for gas exchange? ________[CO2] in indicator Cabomba caroliana more acidic pH 7.6 Atmospheric [CO2] level ___________ [CO2] in indicator more alkaline pH 9.2 7 The fate of photosynthetic products Glucose made in the leaves is transported as sucrose in the phloem vessels. This is possible as sucrose is soluble. This is called translocation. Glucose Amino acids energy used to turn sugars, nitrates & other nutrients into amino acids which built up protein Energy Starch used immediately to provide energy source for respiration to make fats & oils (energy stored in seeds) Sucrose Energy stored as sucrose (in fruit) Cellulose cell wall to make cellulose, the main structural materials in cell wall Factors that affect the rate of photosynthesis Photosynthesis is a process tat needs light, warmth, carbon dioxide. If one of these factors is in short supply, it will limit the rate of photosynthesis, and so is called a limiting factor. light intensity The rate of photosynthesis increases with light intensity. As light intensity ___________, the rate increases up to a _____________ point and plateaus. This is because the rate is limited by other factors. These other factors are _________________ or _________________. [CO2] The rate of photosynthesis increases with carbon dioxide. As carbon dioxide concentration increases the rate increases up to a saturation point and plateaus. This is because the rate is limited by other factors. These other factors are light intensity or temperature. temperature The rate of photosynthesis increases with temperature. As temperature increases the rate increases to optimum temperature. This is because enzymes are denatured by heat. Rate then drops at a rapid rate. 8 Can we regulate these factors to enhance photosynthesis? How do greenhouses work? http://www.aginnovators.org.au/ne ws/protected-cropping-way-future What are the advantages of growing vegetables in greenhouses? 9 What is the importance of minerals to plants? Plants make sugar by absorbing water. In order to stay healthy, plants also need minerals. • Plants absorb minerals from the soil in the form of ions. Uptake of minerals • The elements that the plants obtain from the mineral ions can be divided into two types: major elements and trace elements. • Major elements are needed in a relatively large amount; trace elements are needed in a very trace amount. Questions: 1. Plant grow faster in the summer. Why don’t plants grow in the winter? 2. A farmer grew lettuce in one half of a glasshouse and kept pigs in the other half. He claimed to have a better crop of lettuce as a result. Can you explain why? 10