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PBL- WHEN NATURE
STRIKES
Group members:
Wong Siew Ching D20091034815
Chew Mei Ping D20091034816
Ong Shwu Chyn D20091034817
Yee Hon Kit D20091034822
Ngang Huey Chi D20091034861
TBF 3023Plant Physiology
HOW CACTUS AND BROMELIADS CAN GROW WELL UNDER DRY CONDITION?
Cacti -most water-resourceful plants in the world Pineapple- highly tolerant of drought.
Drought tolerant refers to the degree to which a plant is adapted
to arid or drought conditions. drought tolerant plants typically make use of
either C4 carbon fixation / crassulacean acis metabolism (CAM) to fix carbon during photosynthesis.
Both cactus and bromeliads are CAM plants.
WHAT ARE THE CHARACTERISTIC OF CACTUS AND BROMELIADS?
THE CHARACTERISTICS THAT HELP THEM TO SURVIVE IN DROUGHT.
Cactuses Criteria Bromeliads
Leaves on most cacti are absent or extremely tiny
Leaves ~The epidermis of leaf is especially thick and tough to resist damage and desiccation.~A special layer of water storage cells on the underside of the leaf that act as a reserve in times of water stress~have tiny scales on their leaves called trichomes.
The cactus stem serves as the plant's main photosynthetic organ and is used for water storage
Stem Have distinctive, water-absorbing scales
. Their thinness and large surface area
make the scales ideal for rapidly absorbing
water.
Cactuses Criteria Bromeliads
Cactus roots help to gather and preserve water in several ways .
Roots Able to resist wilting
open their stomates at night rather than during the day in hot or dry climates(CAM Photosynthesis)
Stomata Opens its stomata during the night rather than the daytime(CAM Photosynthesis)
•Spines•Skin
Others •Xerophytes
BROMELIADS LEAVES Unique shape and arrangement of the leaves of
bromeliads. Wide and deeply U-shaped where they join the stem,
forming a series of vessel-like compartments. When it rains, water flows down the leaves and pools in
the compartments, where it can be absorbed by the umbrella scales.
Remarkable "tank plants" - Nidularium and Billbergia. Greatly reduced stem & densely packed leaves have broad, overlapping bases, resulting in a pitcher or vase-like center-the tank. Rainwater fills the tank ,as the tank is shaded by the dense crown of leaves around it, the water does not evaporate quickly and can persist, enabling the plant to survive periods of drought
CACTUSES ROOTS
Shallow & extensive root systems Spread laterally away from the plant. Maximize water intake from a large area.
Change characteristics as the water supply fluctuates. Existing dehydrated roots become more water
conductive after rainfall. Formation of new rain roots to help soak up water. In times of drought, the rain roots shrivel and fall
off .The existing roots dehydrate. The shrinkage of the existing roots creates an air gap
that helps to prevent water in the roots from escaping back to the soil.
A corky layer on the roots also helps to prevent water loss.
SPINES OF CACTUS Spines help the cactus in several ways.
Protection against foragers. Water from dew condenses on spines and, in some
cactus species, downward-pointing spines help to direct rainwater to the roots of the plant.
Reflect light away from the cactus stem theoretically lowering the stem temperature.
Trap in a layer of air next to the cactus stem preventing loss of water via evaporative cooling.
SKIN OF CACTUS
Translucent & acts as the first line of defense against fungi, bacteria, and foraging animals.
The skin has two parts: the epidermis and the hypodermis. The skin's hypodermis layer provides mechanical support for
the plant. A waxy layer of cells known as the cuticle covers the
skin’s epidermis. The wax in the cuticle helps the stem to hold in its water
vapor reducing water loss. Waxy cuticle is also lightly colored and reflects some of the
incident light. Contains numerous stomata
(However, is less than the number for normal plants - another water-saving characteristic.)
XEROPHYTES Possess many of the usual, water-conserving
adaptations of such plants: A thick epidermis covered with wax Water-storage cells that cause the leaves to
appear succulent (that is thick and fleshy Sheathing leaf bases.
Light Dependent Reactions
Non-cyclic photophosphorylation
Cyclicphotophosphorylation
Light Independent Reaction:
Calvin Cycle
HATCH – SLACK PATHWAY
Only occurs in C4 plants and CAM plants.
COMPARISON BETWEEN C3 , C4 , AND CAM PLANTS
EXAMPLES
C3 plants C4 plants CAM plantsTomatoLegumeTobaccoWheat
SugarcaneMaizeSorghumEleusine
CactusBromeliad
CO2 FIXATION AND CO2 ACCEPTOR
C3 plants C4 plants CAM plants
Once, only in mesophyll cells.
Twice, first in mesophyll cells and then in bundle sheath cells.
Once, only in mesophyll cells.
Ribulose biphosphate RuBP (5C) –mesophyll cells
Phosphoenelpyruvate PEP (3C) -mesophyll cellsRibulose biphosphate RuBP (5C) –bundle sheath cells
Phosphoenelpyruvate PEP (3C) -mesophyll cells
ENZYME AND FIRST PRODUCT FORMED
C3 plants C4 plants CAM plants
RuBP carboxylase-inefficient at low CO2 concentration.
PEP carboxylase-high affinity for CO2 at low concentration
RuBP carboxylase-efficient at high CO2 concentration.
PEP carboxylase-high affinity for CO2 at low concentration
Glycerate 3-phosphate (GP), a C3 acid.
Oxaloacetate, a C4 acid.
Oxaloacetate, a C4 acid.
PHOTORESPIRATION
CO2+RuBP(5C) 2G3P (3C) O2+RuBP(5C) phosphoglycorate (2C)+G3P
(3C) Phosphoglycorate was the react with O2 to
form CO2 with no production of energy Is wasteful
PHOTORESPIRATION-O2 IS USED, CO2 IS RELEASED
C3 plants C4 plants CAM plants
Occurs.Oxygen acts as competitive inhibitor.
Inhibited by high concentration of CO2.Light intensity & temperature are higher, O2 is not a competitive inhibitor.
Inhibited by high concentration of CO2.
EFFICIENCY OF PHOTOSYNTHESIS
C3 plants C4 plants CAM plants
Less efficient photosynthesis than C4 plant.Yields usually lower.
Photosynthesis more efficient.Yields are usually much higher.
Photosynthesis more efficient.
LEAF ANATOMY
C3 plants C4 plants CAM plants
Two distinct tissues:•palisade cell•mesophyll cellKrantz anatomy absent1 type of chloroplast in mesophyll cellsVascular bundle packed tightly, many chloroplasts
Vascular bundle surrounded by two rings of cells:•mesophyll cell•bundle sheath cellThinner than C3 plant
Krantz anatomy absent 1 type of chloroplast in mesophyll cells
CROSS-SECTIONS OF LEAVES FROM C3 AND C4 PLANTS.
THANK YOU..