biology plants

• Chlorophyll in the chloroplasts of plant cells absorbs light energy to power photosynthesis.
• Carbon dioxide and water are converted into glucose and oxygen in photosynthesis.
• The xylem transports water from the roots to the leaves, while phloem transports sugars made by photosynthesis.
• Plants use chlorophyll to absorb sunlight, which they then use to produce glucose through photosynthesis.
• Carbon dioxide (CO2) enters through small pores called stomata on the undersides of leaves, while oxygen (O2) diffuses out through these same openings.
• The equation for photosynthesis is carbon dioxide + water → glucose + oxygen
• Purpose of a large surface area for a leaf blade is to increase surface area to volume ratio to obtain max volume of sunlight for photosynthesis
• Stomata are found on the lower epidermis of the leaf
• Which structure of the leaf does not contain chloroplast?

  Epidermis
• List the internal structure of the leaf in order

  1. Upper epidermis
  2. Palisade mesophyll
  3. Spongy mesophyll
  4. Lower epidermis
  5. Cuticle
  6. Stomata
  7. Guard cells
• What is the difference in function of spongy mesophyll and palisade mesophyll?

  Palisade mesophyll : contains the most number of chloroplasts for photosynthesis

  Spongy mesophyll : has a lot of air spaces available as it is the main site for the exchange of gases
• Xylem : carries water and mineral salts

  Phloem : carries sucrose and amino acids
• Waxy cuticle - prevents water loss and is transparent for light to enter the leaf for photosynthesis
• What happens to stomata in the day/presence of sunlight

  Since the guard cells have a lower water potential than the surrounding cells, water enters the guard cells via osmosis. The guard cells become turgid and curve outwards thus opening
• What happens to stomata at night/hot sunny day

  Since the guard cells have a higher water potential than the surrounding cells, water leaves the guard cells via osmosis. Thus, as the guard cells lose water, they become flaccid and curve inwards and close.
• How does CO2 enter the leaf?

  Done via diffusion

  1. CO2 diffuses from surrounding air through the stomata
  2. CO2 dissolves in the thin film of moisture from the surfaces of the mesophyll
  3. Dissolved CO2 diffuses into the cells
• How does water enter the leaf?

  Done via osmosis

  1. xylem transports water and mineral salts from roots to leaves
  2. water and mineral salts move from cell to cell
• XYLEM function : conduct water and mineral salts smoothly

  Adaptations?

  1. empty lumen = xylem is a long hollow tube
  2. lack of cross-walls = lowers water resistance to water flowing through the xylem
• XYLEM function : provide mechanical support

  Adaptations?

  1. inner walls are strengthened by deposits of lignin
  2. lignin prevents vessel from collapsing
• What is lignin?

  hard and rigid substance
• PHOLEM function : conducts sucrose and amino acids from leaves to other parts of the plant

  Adaptation?

  1. cross walls have a lot of minute pores = increases rate of sucrose and amino acids being transported
• Why is the xylem considered a dead cell?

  It is made up of many dead cells as it does not contain nucleus, mitochondria and cytoplasm
• Why is the phloem considered a living cell?

  It is made up of a row of living cells and it has a companion cell that has nucleus and mitochondria
• Name 2 functions of the xylem

  1. Conduct water and mineral salts from roots to leaves smoothly
  2. Provide mechanical support
• Organisation of vascular tissues in leaves

  Inside : Xylem

  Middle : Cambium

  Outside : Phloem
• What is the vascular bundle?

  xylem + cambium + phloem
• True or false?

  Xylem is closer to the lower surface of the leaf

  False
• True or false?

  Phloem is found on the outside of the vascular bundle

  True