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CHAPTER 6: PLANT NUTRITION (Photosynthesis (Part of a leaf: 0001 (The…
CHAPTER 6: PLANT NUTRITION
Photosynthesis
Introduction
Light energy captured by
chlorophyll
(green pigments) in
chloroplast
of a leaf.
Photosynthesis: a process of utilising
light energy
to
convert carbon dioxide and water
into carbohydrate
(sugar) and oxygen
.
Balanced equation of photosynthesis:
6 CO2 (carbon dioxide) + 6 H2O (water) :arrow_right: C6H12O6 (glucose) + 6 O2 (oxygen)
Part of a leaf:
The
most important part
for photosynthesis:
palisade mesophyll cells
(abundance of chlorophyll)
.
Epidermis
: Upper and lower surface of leaf - covered with cuticle (wax).
Mesophyll
: 2 layers of cells (middle of leaf)
top - palisade cells (tall, rectangular shaped)
bottom - spongy cells (air spaces in between cells)
Stomata
: gaps surrounded by
2 guard cells
able to open or close stomata to control water loss during transpiration.
situated at the bottom surface of the leaf.
Vascular bundles
:
xylem vessels
&
phloem vessels
xylem vessels (top part) - carry
water
to leaf (and other parts of the plant)
phloem vessels (bottom part): transport
synthesized products
(sugar) from leaf to other part of plants.
Other cells that also
do
photosynthesis:
spongy mesophyll cells
guard cells
Cells that
do not
do photosynthesis:
Epidermis cells
(keep cells transparent for light to pass through)
Xylem & phloem cells vessels
(specialized in transportation within plants)
Chloroplast
Converting: carbon dioxide + water :arrow_right: sugar + oxygen
Mobile - able to move into position in the cells to comply needs of the plant.
How chloroplasts get their needs:
carbon dioxide: external environment :arrow_right: through stomata :arrow_right: through air spaces (between spongy mesophyll cells :arrow_right: through cell walls :arrow_right: into cell membrane :arrow_right: chloroplast
'Materials' needed for photosynthesis
Water supply
absorbed by root (root hairs)
transported throughout the plants via xylem vessel
Carbon dioxide supply
obtained from the air (0.04%)
CO2 around the chloroplast is lower than CO2 around the leaves (causing concentration gradient for CO2) :arrow_right: net diffusion of CO2 into the leaves (through stomata)
Sunlight supply
sunlight passes through epidermis cells (transparent) and into mesophyll cells (contain most number of chloroplasts)
Factors affecting photosynthesis
Amount (intensity) of sunlight reaching the plant's leaves
When sunlight is a limiting factor: the plant photosynthesizes, but can photosynthesizes faster when being given more sunlight
(Graph drawn will be ascending exponentially)
When sunlight is no longer a limiting factor: the plant is synthesizing as fast as it can (reached maximum point) and cannot utilizes anymore of the extra sunlight
(Graph drawn will be static)
Concentration of carbon dioxide available in the air
When CO2 is the limiting factor: the plant photosynthesizes, but can and will photsynthesizes faster when being fed with more CO2
(Graph drawn will be ascending exponentially)
When CO2 is no longer a limiting factor: the plant photosynthesizing as fast as it can (reached maximum point) and cannot utilizes anymore of the extra CO2
(Graph drawn will be static)
Availability of water
Needed appropriate amount of water (not flooding the plant's roots & no dry-looking soil)
Nutrients (Elements) for Plants
Macronutrients
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Synthesis of nucleic acids, proteins, chlorophyll & enzymes for photosynthesis & respiration.
[Lacking: Chlorosis - synthesis of chlorosis is inhibited]
Phosphorus (P)
Synthesis of nucleic acids, adenosine triphosphates (ATP), & phospholipid bilayers (cell membranes).
[Lacking: Poor root growth - ATP is needed in root cells for active transport of ion]
Potassium (K)
Protein synthesis, carbohydrate metabolism & cofactors for many enzymes.
[Lacking: Stunted growth & yellowing of leaves at the edge - due to reduced protein synthesis, weak cell walls & limited number of working enzymes]
Calcium (C)
Major constituent of middle lamella of cell walls, formation of spindle fibers during cell division.
[Lacking: Stunted growth & distorted/cupped leaves - necrosis & difficulties in cell mitosis]
Magnesium (Mg)
Synthesis of chlorophyll & enzymes activators.
[Lacking: Interveinal chlorosis - lacking of chlorophyll]
Sulphur (S)
Synthesis of certain amino acids, nucleic acids, Vitamin B & some coenzymes.
[Lacking: general yellowing of affected leaves or whole plants.]
Micronutrients
Boron (B)
Aids in calcium ion uptake (in roots) & translocation of sugar molecules, normal cell division (mitotic division), as a cofactor for chlorophyll synthesis.
[Lacking: death of terminal buds - unavailability of B in new parts; Leaves become thick, curled & brittle - abnormal plant growth; Slight yellowing in some plants - chlorophyll synthesis]
Copper (Cu)
Important components of enzymes, metabolism of carbohydrate & nitrogen, lignin synthesis.
[Lacking: Stunted growth & death of young shoots - lignin synthesis unavailable causes cell walls weakening]
Iron (Fe)
Cofactor in the synthesis of chlorophyll.
[Lacking: yellowing of plants, particularly young shoots - due to insufficient production of chlorophyll]
Manganese (Mn)
Enzyme activator in photosynthesis, respiration & nitrogen metabolism.
[Lacking: Green veins on light green leaves - due to disturbed photosynthesis; necrosis (brown spots) in leaves which leads to premature death of shoots.]
Molybdenum (Mo)
Involved in nitrogen fixation (nitrate reduction for protein synthesis).
[Lacking: Reduction in crop yields - nitrogen unavailable causes decreased pollen formation/irregular-shaped leaves/chlorosis or necrosis leaves]
Zinc (Zn)
Formation of leaves, synthesis of auxin (growth hormone).
[Lacking: Mottled leaves with irregular areas of chlorosis - due to leaves unable to properly formed; Retarded growth - lacking of auxin]
