Biology IGCSE - Plant Nutrition

Chloroplast

Organelle found in cells of green parts of plants (leaves and stems) which contain a green pigment called chlorophyll where photosynthesis occurs

Chlorophyll

a green pigment that is found in chloroplasts

Stomata

Controls gas exchange in the leaf.

Stomata open

In light → guard cells absorb water by osmosis → become turgid (swollen) → stoma opens

Stomata closed

In dark → guard cells lose water → become flaccid (shrunken) → stoma closes.

Photosynthesis

the process which plants manufacture carbohydrates from raw materials using energy from light

Word equation for photosynthesis

carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll)

Balanced chemical equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Need for chlorophyll in photosynthesis

Chlorophyll is vital for absorbing light energy → transfers into energy in chemicals → to synthesis carbohydrates

Need for light in photosynthesis

absorbed by chlorophyll → requires light energy to make carbon dioxide and water react to produce glucose and oxygen.

Need for carbon dioxide in photosynthesis

carbon dioxide is transformed into energy (sugars in the form of glucose) → used to synthesis glucose

Different uses and storage of glucose made in photosynthesis: 

(a) starch as an energy store 

(b) cellulose to build cell walls 

(c) used in respiration for energy 

(d) sucrose for transport in the phloem 

(e) nectar to attract insects for pollination

Importance of nitrate ions for making amino acids 

Use in plants:	Importance:	Symptoms of deficiency:
making amino acids	needed to make protein → healthy growth	yellow leaves, weak growth

Importance of magnesium ions for making chlorophyll

Use in plants:	Importance:	Symptoms of deficiency:
making chlorophyll	forms central ion in chlorophyll molecule	yellow leaves between veins of leaves

Limiting factor

something present in the environment in such short supply that it restricts photosynthesis from going faster. Light intensity, carbon dioxide concentration and temperature → limiting factors of photosynthesis.

Understand and describe the effects of varying light intensity on the rate of photosynthesis

Light energy required for photosynthesisn → chlorophyll traps light energy → transfers it into chemical energy. Increase light intensity → increasing rate of photosynthesis

Levels off → another factor limiting photosynthesis or all chlorophyll is being used at any one time and cannot trap anymore light.

Understand and describe the effects of varying carbon dioxide concentration on the rate of photosynthesis

CO₂ is a reactant → requirement of photosynthesis Increasing carbon dioxide concentration → increase rate which carbon is incorporated into chemical reaction → rate of photosynthesis increases

Levels off → another factor limiting photosynthesis.

Understand and describe the effects of varying temperatures on the rate of photosynthesis

Photosynthesis → controlled by enzymes

Reactions speed up → more kinetic energy. 

After optimum temp. → enzymes are denatured → less frequent successful collisions

Hydrogen carbonate indicator with more CO₂

More yellow → more CO₂ present

Respiration happening more than photosynthesis

Hydrogen carbonate indicator with less CO₂

More purple → less CO₂ present

Photosynthesis happening more than respiration

Understand and describe the effect of greater light intensity conditions on gas exchange in an aquatic plant using hydrogencarbonate indicator solution

Greater light intensity → greater rate of photosynthesis → carbon dioxide being used for photosynthesis → colour would be purple

Understand and describe the effect of lower light intensity conditions on gas exchange in an aquatic plant using hydrogencarbonate indicator solution

Lower light intensity → lower rate of photosynthesis → no light → respiration occuring → greater carbon dioxide concentrations → colour would be yellow

Most leaves have a large surface area and are thin

larger surface area → exposed to more light → maximise light absorption

thin → carbon dioxide + oxygen has shorter distance to diffuse → diffusion occurs at a faster rate

thin → light able to penetrate + reach all cells in the leaf

Structure of a leaf

Waxy Cutcile

 

Features	Chloroplast	Function
1. Transparent 2. Waxy	X	1. Reduce water loss from upper surface of leaf 2. allow light to penetration

Chloroplasts

Features	Function
1. contains chlorophyll	1. absorbs light energy for photosynthesis

Guard cells and stomata

Features	Chloroplast	Function
1. Inner surface is very thick 2. contain few chloroplast	Few	1. Allow gas exchange 2. reduce water loss (guard cells open and close stomata)

Upper epidermis

Features	Chloroplast	Function
1. transparent 2. closely - fitting	X	1. allow light to penetrate 2. secrete waxy cuticle 3. Prevent the entry of bacteria and fungi

Lower epidermis

Features	Chloroplast	Function
1. transparent	X	1. allow light to penetrate 2. secret waxy cuticle 3. Protect leaves from pathogens

Palisade mesophyll

Features	Chloroplast	Function
1. Near light - source 2. Closely packed 3. Contain many chloroplast	Many	Layers of cells packed closely together and contains chloroplast to photosynthesis

Spongy mesophyll and air space

Features	Chloroplast	Function
1. Loosely packed 2. Many air spaces 3. Contain few chloroplast	Few	1. Gas exchange to occur inside the leaf 2. Photosynthesis

Vascular bundle (phloem and xylem)

Features	Chloroplast	Function
Upper: xylem - water + mineral ions Lower: phloem - sucrose + amino acids	X	1. Supports the leaf 2. Transports water and organic substances to and from leaf