Biology HL- Plant Biology Flashcards
(41 cards)
Flower
Reproductive unit of angiospermophyte
Pollination
Transfer of pollen from anther to stigma
Cross Pollination
Transfer of pollen between different flowers
Why is cross-pollination preferred?
Leads to greater variation in next generation
Mutualism
Close association between two organisms where both organisms benefit from the relationship:
- animal: gains food in form of nectar
- plant: successful pollination
What does flowering involve?
It involves a change in gene expression in the shoot apex.
Floral initiation is caused by growth and differentiation of apical cells
Cells in the shoot apex change how they divide and differentiation to due to changes in their gene expression
The trigger for the change in gene expression varies but common one is photoperiod
What is transpiration
The loss of water vapor from the leaves and stem of plants
Xerophytes
Plants that can tolerate dry conditions
Adaptions of Xerophytes
- Reduced leaves- reduces total number and size of leaves will reduce the SA available for water loss
- Low growth- Less exposed to winds and more likely to be shaded which would reduce water loss by a decreased rate of transpiration
- CAM physiology- Open their stomata at night reducing water loss via evaporation
- Thick, waxy cuticle- Leaves covered by a thickened cuticle prevents water loss from leaf surface
Halophytes
Plants that can tolerate salty conditions
Adaptions of Halophytes
- Alternate Flowering Schedule- Flower at specific times (e.g. rainy seasons) to minimize salt exposure
- Root Level Salt Exclusion- Roots structured to exclude around 95% of salt in soil solution
- Tissue Partitioning- Concentrate salt in particular leaf, then drop leaf (abscission)
What is a potometer?
A device that is used to estimate transpiration rates indirectly by measuring the rate of water uptake
Factors Affecting Transpiration
Temperature:
Increasing the ambient temperature causes an increase in the rate of transpiration
Higher temperatures lead to an increase in the rate of water vaporisation within the mesophyll, leading to more evaporation
The effect of temperature variation can be tested experimentally by using heaters or submerging in heated water baths
Humidity:
Increasing the humidity causes a decrease in the rate of transpiration
Humidity is the amount of water vapour in the air – less vapour will diffuse from the leaf if there is more vapour in the air
The effect of humidity can be tested experimentally by encasing the plant in a plastic bag with variable levels of vapour
Light Intensity:
Increasing the light intensity to which a plant is exposed is predicted to cause an increase in the rate of transpiration
Increasing light exposure will cause more stomata to open in order to facilitate photosynthetic gas exchange
The effect of light intensity can be tested experimentally by placing the plant at variable distances from a lamp
Wind Exposure:
Increasing the level of wind exposure is predicted to cause an increase in the rate of transpiration
Wind / air circulation will function to remove water vapour from near the leaf, effectively reducing proximal humidity
The effect of wind can be tested experimentally by using fans to circulate the air around a plant
How does a potometer work?
As transpiration occurs, a bubble of air moves into the tube, towards the plant
How do you model water transport in xylem.
Capillary tubing, filter or blotting paper and porous pots
Capillary Tubing:
Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action)
This is due to a combination of surface tension (cohesive forces) and adhesion with the walls of the tube surface
The thinner the tube or the less dense the fluid, the higher the liquid will rise
Xylem Function and Structure
- Xylem Cells contain no cytoplasm provides a larger lumen making water transport more efficient
- Walls impregnated with lignin to strengthen xylem walls preventing its collapse under low internal pressure
- Xylem cells arranged end to end to form continuous vessels, the reduction of walls between cells in a vessel makes it easier for water to move between cells
What is the process of water transport in the xylem and why?
Passive Transport because xylem cells are non-living
How is water transported in the xylem?
Water in mesophyll heated by sunlight and becomes water vapor, which transpires out of stomata
The evaporation causes a negative pressure within the xylem vessel and a transpiration pull
-Cohesion is due to water being a polar molecule in which the oxygen of one water molecule is attracted to the hydrogen a neighboring water molecule
- Adhesion occurs between water and hydrophilic part of cell wall
- As a result of both water can be puled up in xylem as continuous stream
How is water absorbed?
Water is absorbed into root cells by osmosis.
Contrast Apoplast pathway with Sympast pathway
Apopast- Water in root travel through xylem through cells wall
Sympast- Water in root travel through xylem through cytoplasm
Stomata Closed vs Stomata Open
Stomata Closed-
Low concentration of C02/ Low water loss
Low pressure in cytoplasm
Guard cells flaccid
Stomata Open-
High concentration of C02/ High water loss
High pressure in cytoplasm
Guard cells turgid
What causes closing/ opening of stomata?
Closing:
- Water Shortage- Hormone absisicus forces closure of stomata to prevent dehydration
- Darkness
Opening:
High photosynthesis/sunlight
Low CO2 concentration
Active translocation
Transport of organic solvents in plants
Is translocation an active/ passive process
Active as pressure gradient needs to be generated
