Plant Nutrition (B6)

IGCSE biology: B6.1: Photosynthesis B6.2: Leaf Structure

Define photosynthesis

The process by which green plants make carbohydrates and oxygen from carbon dioxide and water, using energy from light

What two conditions are needed for photosynthesis?

Light and chlorophyll

What is chloroplast? 

An organelle present in the plant cell, where photosynthesis takes place

What is chlorophyll?

A green pigment in the plant cells’ chloroplast that absorbs light energy

What is the word equation for photosynthesis?

Carbon dioxide + water —> glucose + oxygen

What is the balanced chemical equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

How are carbohydrates (glucose) used as an energy source?

Plants use glucose (source of chemical energy) to carry out various activities. Some of the glucose produced by photosynthesis is broken down in respiration to release energy

How are carbohydrates (glucose) used for storage?

Glucose is converted into sucrose to become a more stable molecule before being transported in the phloem to different parts of the plant. The sucrose can be changed back into glucose easily. Plants can also convert glucose into starch, which is stored in chloroplasts and cytoplasm and acts as an energy store

How are carbohydrates (glucose) used for structural support?

Glucose is converted into cellulose, which is an important part of the cell wall

How are carbohydrates (glucose) used to assist pollination?

Glucose is used to make nectar, a sweet liquid that attracts animals like insects and birds, these animals in turn, help with pollination

What are minerals?

A group of inorganic substances, formed by the natural breakdown of rocks, essential in organisms to allow them to carry out various functions

What are the mineral requirements for photosynthesis and plant respiration?

Minerals form charged particles (ions) which are then absorbed by root hair cells in the plant root

What are the uses of mineral ions?

Plants use magnesium ions for making chlorophyll (there is a magnesium ion at the center of each chlorophyll molecule, which is essential for the proper function of chlorophyll). Plants use nitrate ions from the soil to make amino acids (the amino acids are then used by plants to make the proteins they need)

What is the effect of light on photosynthesis?

Without light, photosynthesis cannot occur. The rate of photosynthesis increases as light intensity increases (up until a certain point). The certain point is shown by the plateau (flat area) of the graph

What is the effect of carbon dioxide on photosynthesis?

Without carbon dioxide, photosynthesis cannot occur. The rate of photosynthesis increases as carbon dioxide concentration increases (up until a certain point). A certain point is shown by the plateau (flat area) of the graph

What is photosynthesis controlled by?

Enzymes

What is the effect of temperature on photosynthesis?

Photosynthesis is controlled by enzymes, which work best at their optimal temperatures. As temperature increases, the rate of photosynthesis increases (up until a certain point). After that point, the rate of photosynthesis decreases due to the denaturation of the enzyme. The optimum temperature for plants varies between species, but is usually between 20-30 degrees Celsius

What is the word equation for aerobic respiration?

glucose + oxygen —> carbon dioxide + water + ATP

Why can photosynthesis and aerobic respiration be called opposite processes? 

Because photosynthesis uses carbon dioxide and releases oxygen, while aerobic respiration uses oxygen and releases carbon dioxide. Also aerobic respiration happens continously in plant cells, but photosynthesis only happens in the presence of light

What do plants use when they are kept in the dark and cannot photosynthesize?

Starch reserves and are said to be destarched

What do you predict about gas exchange when at a low light intensity? 

The rate of aerobic respiration exceeds the rate of photosynthesis, so they give off more carbon dioxide (plants release carbon dioxide at low light intensities). More carbon dioxide: more aerobic respiration, less photosynthesis

What do you predict about gas exchange when at a high light intensity? 

Photosynthesis occurs at a greater rate than aerobic respiration, so they give off more oxygen (plants release oxygen at high light intensities). Less carbon dioxide: more photosynthesis, less aerobic respiration

What is hydrogencarbonate indicator?

Indicator used to estimate carbon dioxide concentration in solutions

At a low carbon dioxide concentration, what would you expect the hydrogencarbonate indicator color to be?

Magenta/purple

At a normal atmospheric carbon dioxide concentration, what would you expect the hydrogencarbonate indicator color to be?

Red

At a high carbon dioxide concentration, what would you expect the hydrogencarbonate indicator color to be?

Orange/yellow

What test can you use to test for the presence of starch stored in leaves?

Iodine test

Why are plants called autotrophs?

Because they use photosynthesis to produce their own food

Describe the pathway of water and mineral salts across the plant

1. In the roots, through the absorbent hairs, the plant absorbs water and mineral salts from the soil

2. The mixture of water and mineral salts is transported by the xylem tissue until it reaches the leaves

3. The leaves take carbon dioxide from the air, which is mixed with the water and mineral salts with the help of solar energy to form food

4. The plant’s food is distributed through the plant by the phloem tissue

Name the adaptation and describe its function in the cuticle

Waxy layer: stops water from evaporating from the leaf

Name the adaptation and describe its function in the upper epidermis

Chlorophyll absorbs light, enzymes, and structures needed for photosynthesis. This is the site of photosynthesis

Name the adaptation and describe its function in the palisade mesophyll layer

Box-shaped cells, packed close together, each having many chloroplasts pushed to the edges to absorb more light. This is the tissue where photosynthesis happens

Name the adaptation and describe its function in the spongy mesophyll

Cells are loosely spaced, which creates air spaces to allow diffusion of gases through the leaf. This is the site of gas exchange

Name the function in the vascular bundle

Contain xylem and phloem

Name the adaptation and describe its function in the xylem

Forms hollow, water-proof tubes made of dead cells that carry water and mineral ions from the roots to the leaf

Name the adaptation and describe its function in the phloem

Consists of sieve tubes, that carry sucrose away from the leaf, and companion cells that provide energy for transport

Name the adaptation and describe its function in the lower epidermis

A thin layer that allows light to pass through and protects the inner cells

Name the adaptation and describe its function in the guard cells

Entry and loss of water due to osmosis they control the opening of the stomata

Name the adaptation and describe its function in the stomata

Size changes depending on the internal/external environment of the plant, they control the diffusion of water vapour and gases in and out of the leaf

Name the function of the air spaces

Allow diffusion of gases through the leaf