bio: #6

plant nutrition **rmmbr to add in soda lime n sodium hydroxide

photosynthesis

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

photosynthesis chemical equation

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

plants’ main uses of carbohydrates

1. respiration

2. storage

3. synthesizing substances

carbohydrates in respiration

• glucose provides energy

• it’s oxidised by respiration

• energy released is used to drive other chemical reactions

carbohydrates in storage

• glucose molecules are stored as starch

• it’s insoluble, doesn’t alter cell’s osmotic potential

carbohydrates in synthesis of other substances

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

what can glucose molecules be used to synthesize?

1. cellulose (cell walls)

2. amino acids (combine nitrogen & sugar)

3. nectar (attract insects for pollination)

what do plants & animals take in/give out?

1. nitrogen

2. oxygen

3. carbon dioxide

gaseous exchange in plants during day

• photosynthesis rate > respiration rate

• carbon dioxide taken in

• excess oxygen given out

gaseous exchange in plants during night

compensation point occurs

compensation point

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

hydrogencarbonate indicator

used to measure carbon dioxide levels

colors of hydrogencarbonate indicator

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

• made of wax which,

  • waterproofs the leaf

  • is secreted by upper epidermis cells

upper epidermis

• cells are thin & transparent to allow light to pass

• 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

vascular bundle

• leaf vein, made of:

1. xylem

• bring water & minerals to leaf

2. 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

importance of broad, flat shape

large surface area for absorption of sunlight & co2

importance of thin leaves

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

importance of large spaces between cells inside leaf

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

importance of many stomata in lower surface of leaf

allow exchange of co2 & oxygen with outside air

importance of 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

importance of branching network of veins

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

importance of 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