Plant Science

• Main factors required for seeds and plants to grow

  • Water
  • Oxygen
  • Appropriate temperature
  • Sunlight
  • Nutrients
  • Space
  • Carbon dioxide
• Seeds have a food store, so it doesn't need to do photosynthesis
• Conditions for the germination of plant seeds & mung bean plants

  1. Appropriate pH level (not too acidic or basic)

  2. Seeds germinate best in dark environments → plants(stems) are positive phototropism → sprout/grow taller to reach for sunlight

  3. Appropriate temperature → heat increases evaporation, decreases moisture

  4. Water → dissolved with minerals/glucose → provides seed with nutrients

  5. Limited space → the plant may sprout and grow faster due to limited room
• Fertilisers


  Used to help with plant growth
• Fertilisers


  • Nitrogen Phosphorus Potassium (NPK) Fertiliser
• Nitrogen


  Necessary for chlorophyll
• Pesticides


  Used to kill unwanted organisms (e.g. bugs)
• Eutrophication


  1. Excess fertilisers are washed into a water source

  2. Causes algal bloom

  3. When this dies, it requires large quantities of O2 to decompose

  4. The algae blocks the sunlight from the surface

  5. Anything that requires sunlight dies

  6. The decomposing bacteria decompose the dead organisms (requires O2)

  7. Consumes large quantities of oxygen → Anything that requires O2 dies
• Problems caused by overusing Pesticides

  • Bioaccumulation (DDT, microplastics, mercury) in organisms
  • Biomagnification in food chains → affecting consumers
  • The quantity is not lethal at first, but they can't process it → harm
• Upper epidermis


  Produces the waxy cuticle (protective layer and prevents water loss) → more transparent which allows sunlight to penetrate through
• Palisade cells


  Filled with chloroplasts to carry out photosynthesis
• Spongy cells


  Spaces between facilitate the exchange of gases
• Guard cells


  Controls the opening and closing of the stomata, allowing the exchange of gases for photosynthesis during the day, and conserves water by reducing the rate of transpiration and water loss at night
• Stomata


  Regulate gas exchange between the plant and environment and control water loss (assisted by the guard cells)
• Plant cell organelles and functions

  • Nucleus: Contains genetic information (DNA) which controls cell activities
  • Cell wall: Gives the cell extra support, defining its shape
  • Chloroplasts: Contains chlorophyll to absorb light energy
  • Vacuoles: Used for storage + contains cell sap (sugar + salt dissolved in water)
• Photosynthesis


  • Plants take in carbon dioxide (CO2) and water (H2O) from the air and soil
  • Endothermic reaction - requires light energy to produce glucose and O2
  • The light energy is absorbed by the chlorophyll (inside the chloroplast)
  • Glucose is used by plants for energy (needed for respiration and growth) and to make other substances. Cellulose is used in building cell walls. Starch is stored in seeds and other plant parts as a food source.
• Photosynthesis


  6CO2 + 6H2O → C6H12O6 + 6O2
• Testing a leaf for starch

  1. Test w/ iodine: orange-brown (iodine solution) → blue-black (iodine+starch)

  2. To do the test, the chlorophyll must be removed by boiling in ethanol
• Limiting factors in Photosynthesis

  • Number of chloroplasts: more chloroplasts = more photosynthesis, but having fewer/limited chloroplasts can limit photosynthesis
  • CO2 concentration: when the maximum amount of CO2 available is uses up
  • Temperature: The rate ∝ temp. until it reaches an optimal level → rate ↓
  • Water/humidity: low humidity → stomatal closure → prevent water loss → ↓CO2
• Light intensity and rate of Photosynthesis

  • As light intensity increases, the rate increases until a constant max. rate
  • The rate could be limited by the number of chloroplasts or carbon dioxide
• Sucrose


  Soluble but not reactive: used for transportation
• Starch


  Not soluble and not reactive: used for storage
• Glucose


  Soluble & reactive: respiration/production of lipids and proteins
• Pollination & Fertilisation


  1. Pollination: the process of transferring pollen from the anther to the stigma

  2. Transferred by insects/birds/mammals (insect-pollinated plant)

  3. Transferred by the wind (wind-pollinated plant)

  4. Fertilisation: Occurs when the pollen nucleus fuses an ovum nucleus in the ovule

  5. Fertilised ovule forms a zygote → divides → develops into a seed
• Plant adaptations to survive in different environments

  • Large surface area → more exposure to sunlight
  • Thin leaves → shorter diffusion path
  • Branches, stalks, stems → holds leaves out to reach sunlight
  • Root hair cells → large surface area = more absorption of water
• Three Types of Trophism: Phototropism - response to light, Hydrotropism - response to water, Gravitropism - response to gravity
• Xylem transports water from roots to leaves through the process of transpiration.
• Phloem transfers glucose produced during photosynthesis throughout the plant.
• Required factors for seed germination:

  • Water
  • Oxygen
  • Appropriate temperature
  • Appropriate pH level
• • Petal: brightly coloured to attract insects/birds/mammals
  • Sepal: protection for the flower as it grows
  • Anther: produces the pollen (male gamete)
  • Stigma: traps the pollen of other plants
  • Ovary: contains the ovule (female gamete)
• Describe how plants are adapted to survive in different environments

  • Large surface area → more exposure to sunlight
  • Thin leaves → shorter diffusion path 
  • Branches, stalks, stems → holds leaves out to reach sunlight
  • Root hair cells → large surface area = more absorption of water