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B3.1B3. Plant Nutrition and Transport

Photosynthesis — Combined Science 0653 - Biology Revision Notes & Topical Questions

10 min read 26 parts Lesson 2 of 11 1 quiz

📚 Combined Science 0653 - Biology Hub / Topical Revision
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B3.1 Photosynthesis — COMBINED SCIENCE notes: Define photosynthesis, state its word equation and describe the role of chlorophyll, the uses of the carbohydrates made and the need for mineral ions.Photosynthesis = the process by which plants manufacture carbohydrates from raw mate…

  • Raw materials
  • Requirement
  • Respiration
  • Amino acids
  • Own molecules
  • Other elements

Part 1 of 8What photosynthesis is

Photosynthesis
Photosynthesis the process by which plants manufacture carbohydrates from raw materials using energy from light.
Raw materials
  • Raw materials carbon dioxide and water.
  • Light is energy, not a substance, so it is not a raw material.
Products
  • Products glucose, with oxygen released as a waste product.

Part 2 of 8Word equation

  • Equation
    • carbon dioxide + water → glucose + oxygen.
    • The reaction needs light and chlorophyll.

Part 3 of 8Chlorophyll

Chlorophyll
Chlorophyll
  • Chlorophyll a green pigment found in the chloroplasts of plant cells.
Colour
  • Colour it reflects green light, which gives plants their green colour.
Function
  • Function it absorbs light energy and transfers it into energy in chemicals for making carbohydrates such as glucose.
Requirement
  • Requirement photosynthesis cannot happen without chlorophyll.

Part 4 of 8Uses and storage of carbohydrates

Starch
  • Starch glucose is converted into starch, an effective energy store.
Cellulose
  • Cellulose glucose is converted into cellulose to build cell walls.
Respiration
  • Respiration glucose is used in respiration to release energy.
Sucrose
  • Sucrose glucose is converted into sucrose for transport in the phloem.
Nectar
  • Nectar sugar is made into nectar to attract insects for pollination.
Lipids
  • Lipids carbohydrates are converted into lipids as an energy store in seeds.
Amino acids
  • Amino acids glucose combines with nitrogen and other mineral ions from the roots to make amino acids for proteins.

Part 5 of 8Why plants need mineral ions

Own molecules
  • Own molecules plants do not eat, so they must make proteins, lipids and DNA themselves.
Other elements
  • Other elements proteins contain nitrogen, and chlorophyll contains magnesium and nitrogen.
Uptake
  • Uptake mineral ions are actively absorbed from the soil by the root hair cells.

Part 6 of 8Mineral deficiencies

Mineral ionFunctionDeficiency symptom
MagnesiumNeeded to make chlorophyllYellowing between the veins of the leaves
NitrateSource of nitrogen for amino acids and proteinsStunted growth and yellow leaves

Part 7 of 8Testing a leaf for starch

  • Reason
    • glucose is quickly used or stored, so a leaf is tested for starch to show where photosynthesis has happened.
    • Starch is stored in the chloroplasts where photosynthesis takes place.
1
Drop the leaf in boiling water to kill the cells and break down the membranes.
2
Heat the leaf in hot ethanol for 5 to 10 minutes to remove the chlorophyll.
3
Dip the leaf in boiling water to soften it.
4
Spread the leaf on a white tile and cover it with iodine solution.
5
Starch is present if the leaf turns blue-black.
  • Safety
    • ethanol is extremely flammable, so turn off the Bunsen burner and heat it in an electric water bath.

Part 8 of 8More from the specification

More from the specification
Identifying the Primary Limiting Factor
  • On a multi-variable rate-of-photosynthesis graph,
    • when increasing light intensity no longer boosts oxygen production, the plateau indicates that carbon dioxide availability or ambient temperature has become limiting.
Experimental Design for Aquatic Plants
  • Submerging Cabomba or Elodea in sodium hydrogencarbonate solution under an inverted funnel allows precise counting of evolved oxygen bubbles per minute as distance from a light source varies.
Leaf Mesophyll Structure and Gas Diffusion
  • Loosely arranged spongy mesophyll cells provide large moist surface areas and extensive intercellular air spaces for rapid carbon dioxide diffusion towards photosynthetic palisade mesophyll cells.
Light intensity
  • The amount of light.
Limiting factor
  • A factor in such short supply that it restricts the rate of a process.
Temperature
  • Average energy of the particles in an object.
Mesophyll
  • The leaf tissue made of palisade and spongy cells.
Concentration
  • Amount of solute dissolved in a volume of solution.
Indicator
  • Substance that changes colour in acids and alkalis.

Key terms

TermMeaning
PhotosynthesisThe process by which plants make carbohydrates from carbon dioxide and water using light energy.
ChlorophyllThe green pigment in chloroplasts that absorbs light energy.
ChloroplastThe part of a plant cell where photosynthesis happens.
GlucoseThe sugar made in photosynthesis.
StarchThe storage carbohydrate in plants, which turns iodine blue-black.
Mineral ionAn inorganic ion absorbed from the soil.
DestarchTo remove stored starch from a plant by keeping it in the dark.

Avoid these mistakes

1
Giving light as a raw material — the raw materials are carbon dioxide and water.
2
Saying plants make oxygen as the main product — glucose is the product and oxygen is a by-product.
3
Saying chlorophyll absorbs green light — it reflects it.
4
Testing a leaf for glucose to show photosynthesis — the leaf is tested for starch.

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