Plant Biology Flashcards
What plant consists of?
- stem
- leaf
- root
What is the function of stem?
- transports organic materials, ions, and water between the roots and leaves
- storages nutrients.
Structure of the stem
- At the top of the stem there is a terminal growing point
- In the axil of each leaf there is an axillary bud (new cells are produced there)
What does leaf consists of and what is its function?
Consists of a leaf blade and it connected to the stem by the leaf stalk
- it is the organ specialized for photosynthesis
What is the function of root?
- anchoring the plant
- site of absorption of water and ions from the soil
What does the stem consists of?
- vascular bundle (xylem- facing the stem inwards and phloem- facing the stem outwards)
- cambium
- cortex
- epidermis
What is xylem?
Xylem is a dead tissue that has no cytoplasm.
Function of xylem
Transports nutrients and water from roots to stem and leaves.
Structure of xylem
- vessel elements that allow for faster movement of water
- tracheid that allows for exchange of water via pits and leads to slower rate of water movement
- lignin thickening in its walls
What is the transport of water and minerals via the xylem called?
Bulk flow transport
Explain bulk flow via xylem
Water and minerals from the soil enter the plant through the epidermis of roots and pass into the vascular bundle. The water and dissolved minerals in the xylem are transported by bulk flow to the veins of the leaves.
What is phloem?
Living tissue that is responsible for active translocation of sucrose and amino acid from source to sink.
Difference between source and sink
- source is a location in a plant where a resource is taken up
- sink is a location where a resource is used.
What is the structure of phloem?
- sieve tubes
- companion cells
- sieve plates
Sieve tubes
they do not have nucleus, mitochondrion, ribosomes and vacuoles. This reduction enables for nutrients to pass more easily through the cell
Sieve plates
They facilitate the flow of fluid from the cell to the sieve tube.
Companion cells
Located alongside each sieve tube element. They help to load sugars into the sieve tube elements and transport sugars to other parts of the plant.
What is the external structure of leaves?
- leaf blade - flattened part of the leaf
- petiole - leaf stalk
- stipules - base of the leaf
What is the internal structure of the leaf?
- upper epidermis
- palisade mesophyll cells
- spongy mesophyll cells
- xylem and phloem
- lower epidermis
- stomata
- guard cells
The function of upper and lower epidermis
protection of the leaf
function of palisade mesophyll cells
contain chloroplast for photosynthesis
function of spongy mesophyll cells
facilitates the movement of oxygen
guard cells and stomata function
- guard cells - close stomata
- stomata - opening in leaves that allow for gas exchange in leaf
2 main transports of water to xylem
- mass flow - apoplastic pathway
- diffusion - symplastic pathway
Apoplastic pathway (mass flow)
This involves the movement of water and solutes through the non-living spaces outside the plasma membranes of plant cells -> to xylem
Symplastic pathway (diffusion)
This involves the movement of water and solutes through the interconnected cytoplasm of plant cells via plasmodesmata. Substances can pass from cell to cell without crossing cell membranes directly -> to xylem
Plasmodesmata - meaning
channels that connect adjacent cells
Explain osmosis process
The transport of water from vacuole to vacuole of the cells driven by the gradient in osmotic pressure.
Casparian strip
Belt made out of waxy material that does not allow the water and dissolved materials cannot cross the endodermis.
Cohesion tension theory
Water is pulled upward in plants due to the cohesive attraction between water molecules and the tension created by water loss through transpiration in leaves. This creates a continuous column of water in the xylem, facilitating upward movement from roots to leaves.
What are the process that allow the materials to pass from the soil to the roots?
- diffusion and mass flow
- aid provided by fungal hyphae
- active transport
Explain the mass flow and diffusion (soil -> roots)
It occurs when there is a higher concentration of mineral outside the root, the mineral moves into the root. They become dissolved and move via water.
Aid provided by fungal hyphae (soil -> roots)
Fungal hyphae forms a cover over the surface of roots. This creates a large surface area available for water and mineral ion absorption.
Active transport from soil to roots
It occurs when there is a higher concentration of mineral ions inside the plant. Proton pumps establish gradients and membrane transports particular materials into roots.
Explain the bulk flow in xylem and phloem
- sugar is loaded to the sieve tubes and that reduces the water potential inside the sieve-tube elements. this causes the tube to take the water by osmosis.
- the uptake of water generates a positive pressure
- the pressure is relieved by the unloading sugar and water is lost at the sink
- xylem recycles water from the sink to source
Explain the transpiration-translocation process
- leaf produces glucose that is converted to sucrose
- companion cells load the sucrose
- water follows from the xylem by osmosis
- organic molecules are unloaded by companion cells and sucrose is stored by starch
- water is released and recycled as the part of transpiration
Translocation
movement of organic nutrients, primarily sugars, from sources to sinks within the plant.
Transpiration
plants lose water vapor from their leaves and stems into the surrounding air through stomata.
Factors affecting translocation rate
- rate of photosynthesis
- rate of transpiration
- concentrations of sugars in phloem
movement of water in plants
- Root Uptake - diffusion, mass flow, fungal hyphae, active transport
- Root to xylem - osmosis, mass flow, diffusion
- Translocation and transpiration
What is the meristematic tissue in plants
it contains small unspecialized cells that can undergo mitosis. After cytokinesis one cell differentiates and the other one stays in the meristem
Function of meristematic tissue
results in the growth of plants
What is auxin?
It is the plant hormone that promotes a tissue growth and it is found in meristems
What is the function of high auxin levels?
Promotes cell elongation in shoots (positive phototropism) and in roots it inhibits the elongation (negative phototropism)
State the definition of tropism
growth toward or away from a directional stimulus in the environment
Positive phototropism
Growth of plant towards the directional source of light. Shoots bend towards light and they become elongated.
Negative phototropism
Growth of plant away from the directional source of light.
Gravitropism
Growth of shoots and the downward growth of roots in response to gravity
What was the Charles and Francis Darwin experiment on sensing light by plants?
They wanted to find out which part of the plant senses light
- They used oat seeds and placed them in the dark for some time to ensure they were straight and vertically oriented.
- they exposed the seeds to a unidirectional light source, such as sunlight or a lamp.
- Over time, they observed that the seeds exhibited a bending response towards the light source.
Structure of flowers
- petal - attracts the insects to flower
- anther - produces male sex cells
- filament - holds anther
- stigma - holds pollen
- style - holds stigma
- ovary - female sex cells
- ovule
- sepal - protects and holds flower
- receptable - holds flower
What is the pollination?
Transfer of pollen from a mature anther to a receptive stigma. We include:
- cross-pollination
- self-pollination
Cross-pollination
pollen is delivered to a flower from a different plant
Self-pollination
pollen from one flower pollinates the same flower or other flowers of the same individual
What is the mutualistic relationship?
Two organisms of different species work together to benefit.
- example: bees and flower - they collect the nectar and flowers are pollinated.
Fertilization
Male and female gametes fuse to form a zygote. This occurs in the ovule of the flower.
Structure of seeds
- cotyledom (storage)
- testa (protects the seed )
- micropyle (scar caused by pollen entering the ovule)
- embryonic root
- embryonic shoot (becomes a new plant when the germination occurs)
Double-fertilization
Fusion of gametes occurs after two sperm reach the female ovule.
Seed dispersal
movement or transport of seeds away from the parent plant. The main modes include:
- gravity
- wind
- water
- animals
Seed germination
Growth of an embryonic plant contained within a seed and it results in the formation of the seeding.
Factors that influence germination
- temperature
- oxygen
- water uptake
Photoperiodism
refers to the physiological response of plants to the relative lengths of day and night.
Short-day plants
flowers at night become longer and during the day they are shorter. they require a continuous period of darkness before flowering
What is the phytochrome?
plants that respond to periods of darkness
Where water evaporates?
mesophyll cells (water moves there from xylem)
What is the potometer used for?
estimating transpiration rates by measuring the rate of water loss
What are the environmental factors that affect the transpiration?
- humidity
- air movement
- temperature
- water supply
- light intensity
How humidity affects transpiration?
the lower the humidity outside of the leaf is, the faster the rate of transpiration.
How air movement affects transpiration?
an increase in air movement increases transpiration
How temperature affects transpiration?
increase in temperature increases transpiration
How water supply affects transpiration?
transpiration is lower if there is a little water available as transpiration depends on the mesophyll walls being wet
How light intensity affects transpiration?
greater light intensity increases the rate of transpiration because it opens stomata
What are the guard cells?
They control the opening and closing of the stomata.
What if the guard cells are flaccid ?
If the guard cells are flaccid, the stomatal pore closes, reducing water loss from the plant but also limiting the uptake of carbon dioxide for photosynthesis.
What if the guard cells are turgid ?
If the guard cells are turgid, the stomatal pore opens, allowing for the exchange of gases such as carbon dioxide and oxygen between the plant and the atmosphere.
Photosynthesis in C4 plants
stomata facilitates the efficient gas exchange for photosynthesis while minimizing water loss, contributing to the plant’s ability to survive in hot and arid environments.
CAM plants
open their stomata during the night and close them during the day. closing it helps the desert plants conserve water and prevents from CO2 entering the leaves.
What is the ABA?
Plant growth regulator that is contained in stems, leaves, and fruits. Its presence assists plant survival during the stress such as drought. In such conditions ABA levels are raised and the water loss is reduced.
