bio: #6

plant nutrition

photosynthesis

process by whichh plants manufacture carbohydrates from raw materials using energy from light

photosynthesis chemical equation

6CO₂ + 6H₂O (light, chlorophyll) → C₆H₁₂O₆ = 6O₂

respiration

glucose provides energy, oxidised by respiration and energy released is used to drive other chemical reactions

storage

glucose molecules are stored as starch as it’s insoluble and doesn’t alter cell’s osmotic potential

synthesis of other substances

starch → sucrose to be transported by leaf veins → plant parts that don’t photosynthesize → glucose

glucose molecules can be used to synthesize

1. cellulose

2. amino acids

3. nectar

compensation point

when there is no net intake or output of oxygen and carbon dioxide

hydrogencarbonate indicator

measure co2 levels

1. red = atmospheric air

2. orange/yellow = co2 increase

3. magenta-deep purple = co2 removed

limiting factor

something present in the environment in such short supply that it restricts life processes

limiting factors of photosynthesis

1. light intensity

2. temperature

3. co2 concentration

leaf structure

1. waxy cuticle

2. upper epidermis

3. palisade mesophyll

4. spongy mesophyll

5. vascular bundle (xylem & phloem vessels)

6. lower epidermis

7. stomata

waxy cuticle

• wax:

  • waterproofs the leaf

  • is secreted by upper epidermis cells

upper epidermis

• cells are thin & transparent to allow light to pass as they are no chloroplasts

• barrier to disease organisms

palisade mesophyll

• main region for photosynthesis

• cells are:

  • columnar

  • packed with chloroplasts to trap light energy

  • receiving CO2 by diffusion from air spaces in spongy mesophyll

spongy mesophyll

• cells:

  • are spherical and loosely-packed

  • contain chloroplasts (lesser than palisade)

  • have air spaces between each other to allow gaseous exchange

    • CO2 → cells, cells → oxygen during photosynthesis

vascular bundle

• leaf vein, made of:

• xylem

  • water & minerals → leaf

• phloem

  • transports sugars & amino acids away (translocation)

lower epidermis

• protective layer

• stomata present to regulate water vapour loss (transpiration)

• site of gaseous exchange in & out of leaf

stomata

• each stoma has a pair of guard cells

  • these control whether stoma is open/close

• water vapour passes out during transpiration

• co2 diffuses in, oxygen diffuses out during photosynthesis

material of xylem

lignin, which strengthens it

shape of phloem

sieve tubes, ends of each elongated cell are pierced to form sieve plates

adaptations of a leaf for photosynthesis

1. broad, flat shape

2. thin leaves

3. large spaces between cells inside leaf

4. many stomata in lower surface of leaf

5. more chloroplast in upper palisade than lower spongy cells

6. branching network of veins

7. waxy cuticle

broad, flat shape

large sa for absorption of sunlight & co2

thin leaves

co2 has to diffuse across short distances to reach inner cells, same for light to reach chloroplast

large spaces between cells inside leaf

easy passage for co2 & oxygen to diffuse in & out of leaf

many stomata in lower surface of leaf

allow exchange of co2 & oxygen with outside air

more chloroplast in upper palisade cells than lower spongy cells

most sunlight will be received by cells, this will reach chloroplast without being absorbed by many cell walls

branching network of veins

xylem provides good water supply to photosynthesizing cells & phloem transports sugars away from leaf

waxy cuticle

redues water loss through evaporation from leaf

important minerals for plants

1. nitrate ions

2. magnesium

nitrate ion function

• make amino acids

• important to make proteins to form enzymes/cytoplasms of cells

nitrate ion deficiency effects

• stunted growth

• weak stem

• lower leaves → yellow

• upper leaves → pale green

magnesium function

• form chlorophyll

magnesium deficiency effects

• leaves → yellow from bottom of stem upwards

  • chlorosis → deficiency of chlorophyll