B5 - Plant nutrition

Question 1

Photosynthesis definition

Answer 1

The process by which plants manufacture carbohydrates (as nutrition) from raw materials using energy from light
- conversion of light energy from the sun into chemical energy

Question 2

Photosynthesis balanced equation

Answer 2

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Question 3

Use of carbohydrates in plants (name 4)

Answer 3

• Converted into starch molecules which act as an effective energy store
• Converted into cellulose to build cell walls
• Glucose can be used in respiration to provide energy
• Converted to sucrose for transport in the phloem
• As nectar to attract insects for pollination
• Converted into lipids for energy storage in seeds
• Combined with nitrate minerals to make amino acids (proteins)

Question 4

Carbon dioxide

Answer 4

• raw material gas found in the atmosphere
• absorbed by stomata of the leaves and used in chloroplasts for photosynthesis

Question 5

Oxygen

Answer 5

• through photosynthesis: water is transformed into oxygen by the movement of electrons
• diffused as a waste product through the stomata

Question 6

Chlorophyll and its function

Answer 6

• Green pigment that is found in chloroplasts within plant cells
  - it is this pigment which gives plants their characteristic green colour
• Transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
  - is essential for photosynthesis to occur

Question 7

Nitrogen ions in plants

Answer 7

• majorly used to make amino acids (the building blocks of proteins)
• are also a part of chlorophyll

Question 8

Magnesium ions in plants

Answer 8

• major component in making chlorophyll in chloroplasts
• therefore necessary in photosynthesis

Question 9

Nitrate ion deficiency in plants

Answer 9

Causes stunted growth and yellowing leaves from a lack of chlorophyll

Question 10

Magnesium ion deficiency in plants

Answer 10

Causes yellowing between the veins of the leaf (chlorosis)

Question 11

Sunlight use in photosynthesis

Answer 11

Provides the initial light energy that starts the process of photosynthesis and is then transferred into chemical energy

Question 12

What effects the rate of photosynthesis? (3)

Answer 12

• light intensity
• carbon dioxide concentration
• temperature

Question 13

Minerals in plants

Answer 13

Nitrogen, magnesium, phosphorus, potassium
- Plants obtain these elements in the form of mineral ions actively absorbed from the soil by root hair cells

Question 14

Protein synthesis

Answer 14

The formation of proteins by using information contained in DNA and carried by mRNA
- happens subsequent to photosynthesis

Question 15

Testing for the presence of starch (5 steps)

Answer 15

• A leaf is dropped in boiling water to kill the cells and break down the cell membranes
• The leaf is left for 5-10 minutes in hot ethanol in a boiling tube. - This removes the chlorophyll so colour changes from iodine can be seen more clearly
• The leaf is dipped in boiling water to soften it
• The leaf is spread out on a white tile and covered with iodine solution
• In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf

Question 16

Investigating the need for carbon dioxide

Answer 16

• Destarch two plants by placing in the dark for a day
• Place one plant in a jar which contains a beaker of sodium hydroxide (which will absorb carbon dioxide from the surrounding air)
• Place the other plant in a jar which contains a beaker of water (control experiment), which will not absorb carbon dioxide from the surrounding air
• Place both plants in bright light for several hours
• Test both plants for starch using iodine
• The leaf from the plant placed near sodium hydroxide will remain orange-brown as it could not photosynthesise due to lack of carbon dioxide
• The leaf from the plant placed near water should turn blue-black as it had all necessary requirements for photosynthesis

Question 17

Investigating the need for light in photosynthesis

Answer 17

• Plant needs to be destarched by placing in a dark cupboard for 24 hours
  
  • this ensures that any starch already present in the leaves will be used up and will not affect the results of the experiment
• Following destarching, a leaf of the plant can be partially covered with aluminium foil (which resists light) and the plant placed in sunlight for a day
• The leaf can then be removed and tested for starch using iodine
  
  • the area of the leaf that was covered with aluminium foil will remain orange-brown as it did not receive any sunlight and could not photosynthesise, while the area exposed to sunlight will turn blue-black

Question 18

Investigating the need for chlorophyll (variegated leaf)

Answer 18

• The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black
• The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored

Question 19

Investigating the rate of photosynthesis (light)

Answer 19

Use a type of aquatic plant:
- put into a boiling tube or an into an inverted funnel in a cylinder with a rotated measuring tube above it
- cut the stem of the pondweed
- move the tube/cylinder near the light source (10cm) and leave it over time to adjust

CASE 1: bubbles
- As photosynthesis occurs, oxygen gas produced is released
- As the plant is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed
- The number of bubbles produced over a minute can be counted to record the rate
- the more bubbles produced per minute, the faster the rate of photosynthesis
- Repeat process over larger distances from light source

CASE 2: volume of bubbles
- The bubbles produced will move up the funnel and collect in measuring tube
- this will take longer time
- give the volume of oxygen

CONCLUSION:
- the further the light source (lower the light intensity) the slower the rate of photosynthesis

Question 20

Investigating the rate of photosynthesis (carbon dioxide)

Answer 20

Use a type of aquatic plant:
- put into an inverted funnel in a cylinder with a rotated measuring tube above it
- cut the stem of the pondweed
- Dissolve starting amount of sodium hydrogen carbonate in water (creates CO2)
- change amount over time and record change

Question 21

Investigating the rate of photosynthesis (temperature)

Answer 21

Use a type of aquatic plant:
- put into an inverted funnel in a cylinder with a rotated measuring tube above it
- cut the stem of the pondweed
- Put a hot plate beneath the cylinder and begin to heat up the water within it (make sure a thermometer is used and all other factors are kept the same)
- change temperature and assess

Question 22

Graph description of limiting factors of photosynthesis

Answer 22

1. Temperature: As temperature increases the rate of photosynthesis increases; as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases

2. Light intensity: The more light a plant receives, the faster the rate of photosynthesis; this trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply (e.g temp.)

3. Carbon dioxide: the more carbon dioxide that is present, the faster the reaction can occur; this trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply

Question 23

Waxy cuticle function and adaptation

Answer 23

Function: protective layer on top of the leaf, prevent water from evaporating

Adaptation: thin and transparent to allow light to pass through it but has a waxy surface to resist osmosis

Question 24

Upper epidermis function and adaptation

Answer 24

Function: the part of the leaf above the palisades layer that prevents the loss of water found above palisade mesophyll

Adaptation: thin and transparent to allow light to pass to palisade layer beneath it

Question 25

Palisade mesophyll function and adaptation

Answer 25

Function: Layer of tall, column-shaped mesophyll cells just under the upper epidermis of a leaf; full of chloroplasts used for photosynthesis

Adaptation: tightly-packed together and full of chloroplasts to maximise light absorption; rectangular shape increases surface area; large vacuole for water storage

Question 26

Spongy mesophyll function and adaptation

Answer 26

Function: layer of loose tissue found beneath the palisade mesophyll in a leaf, widely spaced to allow gas exchange and also acts for photosynthesis

**Adaptation: **contains internal air spaces that increase the surface area to volume ratio for the diffusion of gases

Question 27

Lower epidermis function

Answer 27

Protective layer on the bottom of leaf which contains stomata & guard cells

Question 28

Guard cells function and adaptation

Answer 28

Function: absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in and oxygen to diffuse in

Adaptation: wall of the guard cell is differentially thickened with the inner membrane to open the stoma when turgid; opens in an oval shape to aid diffusion and flattens when closed

Question 29

Stomata function and adaptation

Answer 29

Function: where gas exchange takes place; opens during the day and closes during the night; evaporation of water also takes place

Adaptations: allows different gases to diffuse into separate areas

Question 30

Vascular bundle function and adaptation

Answer 30

Function: contains xylem and phloem to transport substances to and from the leaf

Adaptation: thick cell walls of tissues help to support stem and leaf

Question 31

Xylem function

Answer 31

Transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration through stomata

Question 32

Phloem function

Answer 32

Transport minerals (sucrose and amino acids) around the plant