Photosynthesis & the Carbon Cycle Chapter 1 Learning Outcomes Chapter 1.1 Photosynthesis Chapter 1.2 More About Photosynthesis 01 Photosynthesis Chapter 1.1 Photosynthesis light ● Process that plants undergo to make food (glucose) ● Occurs in the leaves (chloroplast) making 3 Requirements Sunlight Carbon Dioxide Water From Sun From air From soil Photosynthesis ● Energy in sunlight is captured by chlorophyll (green pigment found in chloroplasts) ● Plants use the energy to convert carbon dioxide and water into glucose and oxygen word equation: carbon dioxide + water → glucose + oxygen Importance of Photosynthesis 1. Provides energy ● Provides energy for other organisms in the form of chemical energy (nutrients) ● All the energy in all the food in the world comes from plants ● Plants use energy in sunlight to make glucose and other carbohydrates ● When animals eat food, they gain some of the energy that was captured by plants ● A food chain shows how this energy is passed along from one organism to another Energy Flow in Food Chains Importance of Photosynthesis 2. Provides oxygen ● Provides oxygen for the Earth’s atmosphere ● Animals and plants need oxygen for respiration ● Oxygen is a waste product of photosynthesis ● Oxygen is released from the leaves of plants and mixes with the other gases in the atmosphere ● About 20% of the air in the atmosphere is oxygen Fun Fact! ● When Earth first formed about 4.6 billion years ago, there was almost no oxygen in the atmosphere ● Scientists believe that oxygen first began to collect in the air when bacteria first began to photosynthesise ● There were no plants at that time (plants only appeared on Earth about 4.7 million years ago) ● If photosynthesis had never begun on Earth, no animals would have been able to live here! 02 More About Photosynthesis Chapter 1.2 Chloroplasts ● Photosynthesis occurs in chloroplasts ● Cells in the leaves have the most chloroplasts ● Not all plant cells have chloroplasts (e.g. - root hair cells), so not all plant cells can undergo photosynthesis Chlorophyll ● A green pigment found in chloroplasts ● Essential for photosynthesis ● Function: capture energy from sunlight → helps carbon dioxide and water to react together ● Inside the cells in a leaf, carbon dioxide and water react to produce carbohydrates (glucose) and oxygen Starch 01. Plants make more carbohydrates than they need on sunny days 03. Plants store carbohydrates as starch in chloroplasts 02. Plants store some of the carbohydrates for later use (e.g. at night, days with less sunlight) 04. One way to check if a plant has been photosynthesising is to test it for starch Testing for Starch (Iodine Test) 1 2 3 5 iodine solution 1. Take a healthy leaf from a plant. 2. Carefully drop the leaf into boiling water. This dissolves the waxy cuticle which allows iodine to enter the cells. 3. Turn off the bunsen burner. Use forceps to carefully transfer the leaf into a test tube containing ethanol. Stand the test tube in the hot water to safely heat up the ethanol. Ethanol dissolves the chlorophyll and removes the green colour from the leaf. 4. Remove the leaf from the test tube and rinse it under cold water. 5. Spread out the leaf onto a tile. Add a few drops of iodine solution onto the leaf. The leaf will turn blue-black if starch is present. ethanol 4 Inside a Leaf ● ● Waxy layer Reduces water loss Protects the cells in the leaf ● ● A lot of air spaces (allow gases to diffuse easily) Small amount of photosynthesis ● Contains cells that do most of the photosynthesis* ● Most chloroplasts Carries water to the cells in the leaf ● ● ● Singular: stoma Tiny hole in the lower epidermis Allows gases to diffuse in and out Protects the cells in the leaf *Note: it is easy for sunlight to reach the cells as leaves are very thin Minerals and Plant Growth 01 Farmers add fertilisers to make crops grow larger and produce a higher yield (quantity of crop harvested). 02 Fertilisers contain minerals in which plants need in small quantities. Plants obtain minerals from the soil through their roots. 03 Sometimes the soil does not contain enough of certain minerals, which stops the plants from growing to their full potential. Important Minerals for Plants 1. Magnesium ● Needed to make chlorophyll ● Lack of magnesium: - Leaves look yellow instead of green - Does not have much chlorophyll → cannot photosynthesise as much as it should → cannot grow well Important Minerals for Plants 2. Nitrate ● Contains nitrogen atoms ● Needed to make chlorophyll ● Needed to convert carbohydrates to proteins ● Proteins are essential for making new cells so that the plant can grow well ● Lack of nitrogen: - Leaves die Plant stays small Fun Fact! ● Farmers can test the soil in their fields to find out exactly which minerals are lacking in each part of the field. ● This tells the farmers where they need to add fertiliser and where it is not needed. ● Farmers who can afford the latest technology can use global positioning satellites (GPS) with their machinery. ● The screen in the tractor cab shows the farmer exactly where they are in the field and the results of the soil tests. ● The farmer can easily control how much fertiliser is added in each part of the field. Summary… ● Photosynthesis is a process that plants undergo to make food (glucose) ● Photosynthesis occurs in chloroplasts that are mainly found in leaf cells ● Chlorophyll is a green pigment found in chloroplasts that captures energy from sunlight ● Excess carbohydrates produced by plants are stored as starch ● Magnesium and nitrate are important minerals for plants photosynthesis word equation: carbon dioxide + water → glucose + oxygen The End! Wouldn’t it be cool if humans could make their own food too?
