B1.4 - Photosynthesis

Question 1

What are the reactants in photosynthesis?

Answer 1

Water and Carbon dioxide

Question 2

What is the word equation for photosynthesis?

Answer 2

Carbon dioxide + water -> oxygen + glucose

Question 3

State the balanced chemical equation for photosynthesis

Answer 3

6CO + 6H O -> 6O + C H O

2 2 2 6 12 6

Question 4

Describe the process of photosynthesis (3)

Answer 4

• Carbon dioxide is absorbed from the air, and water is absorbed from the soil. Energy from the sun is converted to light energy.
• those three substances react together to make glucose
• waste products (ie. oxygen) is released into the atmosphere

Question 5

where does photosynthesis occur?

Answer 5

in the chloroplasts of plants

Question 6

why are leaves and stems green?

Answer 6

since they contain chlorophyll

Question 7

what is the role of chlorophyll in plants?

Answer 7

to convert energy from the sun into light that the plant can use

Question 8

What are the two main stages of photosynthesis?

and give a brief description of what happens

Answer 8

Stage 1 - Light Dependent
- when energy transferred from light splits water molecules into hydrogen ions and oxygen gas

Stage 2 - Light Independent
- when carbon dioxide gas combines with hydrogen ions to make glucose

Question 9

what kind of reaction is photosynthesis, and why?

Answer 9

an endothermic reaction (energy is transferred from surroundings to keep it going - ie. energy from sun)

Question 10

How is glucose produced during photosynthesis used? (6)

Answer 10

• respiration
• converted into sugar molecules and stored in fruit
• starch (food stores used at night - when no sunlight)
• cellulose (cell walls)
• proteins (for growth and repair)
• fats and oils (food store + growth)

HINT - don’t need all uses, only correct idea (not in spec)

Question 11

Describe how to test a leaf for the presence of starch

Answer 11

• wash it in boiling water so cell wall breaks down
• place a leaf in ethanol for 1 minute (to remove chlorophyll)
• then wash it under water to get rid of the ethanol + to soften it
• place the leaf on a white tile and add a few drops of iodine on it
• if the leaf becomes black/blue, it contains starch

Question 12

How do you prove that chlorophyll is needed for photosynthesis?

Answer 12

• place a destarched variated leaf (ie. has white and green parts) into sunlight for a few hours
• then test for starch by adding a few drops of iodine
• if plant becomes black-blue = starch is present (chlorophyll present there)
• if leaf stays orange = no starch present (no chlorophyll present there)

Question 13

How do you prove that light is needed for photosynthesis?

Answer 13

• get a destarched leaf and cover half ish with a piece of black card
• place the leaf in sunlight for a few hours
• take the black card off and test for starch

Question 14

How do you prove that Carbon Dioxide is needed for photosynthesis?

Answer 14

• Place a destarched plant in a sealed plastic bag with a pot of soda lime (which absorbs carbon dioxide)
• place the plant in sunlight for a few hours
• test the leaves for starch

Question 15

How do you prove that oxygen if given off during photosynthesis?

Answer 15

• place an upside test tube on a beaker of a sea plant
• as the test tube fills up with air/bubbles, put a glowing splint in the test tube
• it will relight if oxygen is present

Question 16

state three factors which affect the rate of photosynthesis

Answer 16

• temperature
• light intensity
• carbon dioxide concentration

Question 17

describe the effect of light intensity on the rate of photosynthesis

Answer 17

higher the light intensity, higher the rate of photosynthesis

Question 18

how does carbon dioxide affect the rate of photosynthesis?

Answer 18

• greater carbon dioxide concentration, faster rate of reaction

Question 19

how does temperature affect the rate of photosynthesis?

Answer 19

• photosynthesis is an enzyme-controlled reaction
• higher temp, faster reactions
• too high temp, enzyme can denature and reactions stop

Question 20

Describe one way to measure the rate of photosynthesis

Answer 20

• volume of oxygen given off per minute (by pondweed)

- count the number of bubbles produced per minute

Question 21

how do you study the effect of light intensity on the rate of photosynthesis?

Answer 21

pace a light source at different distances from pondweed

Question 22

what is the equation for the relative light intensity?

Answer 22

= 1
————————————
distance from light source^2

Question 23

how do you study the effect of carbon dioxide concentration on the rate of photosynthesis?

Answer 23

• add different masses of potassium hydrogen carbonate powder to water
• potassium hydrogen carbonate powder releases carbon dioxide into atomsphere

Question 24

how do you study the effect of temperature relative to the concentration on the rate of photosynthesis?

Answer 24

• place the apparatus in water baths at different temperatures

Question 25

What is a limiting factor?

Answer 25

When one factor required during photosynthesis is not present, and so the rate of photosynthesis cannot increase

Question 26

Describe the process of photosynthesis

Answer 26

• an endothermic reaction
• use of (sun)light energy
• use of carbon dioxide and water
• produce : glucose / carbohydrate / starch, and oxygen
• use of chlorophyll / occurs in chloroplasts

Question 27

State what is meant by light intensity

Answer 27

the brightness of light / amount of light that a plant receives during photosynthesis

Question 28

using what process do root hair cells absorb water?

Answer 28

osmosis

Question 29

using what process do root hair cells absorb mineral ions?

Answer 29

active transport