Transport in Plants Flashcards
What are the functions of xylem?
Xylem transports water and mineral ions and provides support for the plant’s overall structure.
What are the functions of phloem?
Phloem transports sucrose and amino acids from the source to the sink and vice versa.
What are the adaptations of xylem?
Thick walls with lignin (dead cells)
No cell contents
Cells joined end to end with no cross walls to form a continuous tube
How do root hair cells absorb water?
Root hair cells absorb water by osmosis due to their large surface area, which increases water uptake from the soil.
What is the pathway of water through the plant?
Water moves from root hair cells to root cortex cells, then to xylem, and finally to mesophyll cells in the leaf.
What is transpiration?
Transpiration is the loss of water vapour from the leaves through the stomata.
How does water move during transpiration?
Water evaporates from the mesophyll cells, moves into air spaces, and diffuses out of the leaves through the stomata.
What causes wilting in plants?
Wilting occurs when water loss exceeds water uptake, causing cells to become flaccid and tissues to become limp.
What factors affect the rate of transpiration?
-Temperature: Higher temperatures increase evaporation and diffusion rates.
-Humidity: Low humidity increases transpiration, while high humidity decreases it.
-Wind speed: Wind increases transpiration by removing water vapour and maintaining a steep concentration gradient.
What is translocation in plants?
Translocation is the movement of sucrose and amino acids in the phloem from the source (where they are produced) to the sink (where they are used or stored).
What are sources and sinks in plant translocation?
Sources: Parts of the plant that release sucrose or amino acids.
Sinks: Parts of the plant that use or store sucrose or amino acids.
How does water move through the root to the stem and leaf?
Water enters the root hair cells by osmosis, travels through root cortex cells to the xylem, and moves up the stem to the mesophyll cells in the leaves.
How does water enter and leave cells in plants?
Water enters and leaves cells by osmosis.
How do dissolved substances enter and leave plant cells?
By diffusion and active transport.
What are the roles of water in plants?
Water supports the plant, acts as a reagent in biochemical reactions, and serves as a transport medium.
How do root hair cells absorb minerals and water from the soil?
Root hair cells absorb minerals as ions and water by osmosis.
What is the role of the large surface area of root hair cells?
It helps in efficient absorption of water and minerals.
Give an example of ions absorbed by roots and their forms.
Magnesium as Mg²⁺ ions and nitrogen as nitrate (NO₃⁻) ions.
How can ions enter root hair cells when their concentration is higher inside the cell than in the soil?
Through active transport.
What happens when stomata are open?
Water is lost by evaporation from spongy mesophyll cells.
What is the sequence of water movement through a plant?
- Loss from leaves
- Crossing membranes in the cortex
- Upward flow in xylem (transpiration stream)
- Absorption by root hair cells.
What ensures selective entry of substances into the xylem?
Cell walls contain a waxy material making them impermeable, forcing substances to cross cell membranes.
How does water move across the cortex in roots?
(a) By osmosis through cells
(b) By suction through cellulose cell walls (freely permeable).
Why is soil water absorbed into root hair cells by osmosis?
Because soil water has a higher water potential than the cytoplasm of the root hair cells.
What is the transpiration stream?
The upward flow of water from roots to replace water lost at the leaves.
Why should transplanted plants retain a ball of soil around their roots?
To prevent damage to delicate root hairs, aiding in quicker recovery.
What is osmosis in the context of plant cells?
Osmosis is the movement of water molecules from a region of higher water potential to lower water potential across a partially permeable membrane.
What factors affect the uptake of water by root hair cells?
Water potential gradient and the surface area of root hair cells.
Why is the cytoplasm of root hair cells hypertonic compared to soil water?
The cytoplasm contains dissolved solutes, lowering its water potential compared to the surrounding soil water.
What role do cell walls play in water movement across the root cortex?
Cell walls allow water to move freely through cellulose pathways by suction.
What happens when the water potential gradient is steep?
Water uptake by osmosis is faster.
How do plants absorb minerals when the soil concentration is higher than the root cell concentration?
Minerals diffuse into the root cells down their concentration gradient.
How do plants absorb minerals against a concentration gradient?
By active transport, using energy from ATP.
What is the main energy source for active transport in plants?
ATP, produced during cellular respiration.
Why do plants with damaged root hairs struggle to absorb water?
Root hairs provide a large surface area; damage reduces efficiency in water and mineral absorption.
What is the role of the xylem in water transport?
The xylem carries water upward from the roots to the leaves as part of the transpiration stream.
How does water loss from leaves drive the uptake of water by roots?
Water loss creates a suction force that pulls water upward through the xylem.
What is the significance of the waxy material in some cell walls?
It prevents water from passing freely, ensuring selective absorption through cell membranes.
What is the importance of nitrate ions (NO₃⁻) for plants?
Nitrate ions are used to synthesize amino acids and proteins essential for plant growth.
What is the role of magnesium ions (Mg²⁺) in plants?
Magnesium is essential for chlorophyll production, critical for photosynthesis.
Why do plants have such extensive root systems?
To maximize water and mineral absorption from the soil.
What happens to water potential in plant cells when water enters by osmosis?
The water potential inside the cells increases until it reaches equilibrium with the surrounding environment.
How does the root cortex contribute to water movement?
It transports water via osmosis and cellulose pathways toward the xylem.
What is the primary pathway for water movement across the root cortex?
Route (b): Suction through the freely permeable cellulose walls.
What ensures water absorption from the soil solution into root hair cells?
The water potential gradient between soil water and the cytoplasm of root hair cells.
How do root hairs increase the efficiency of water and mineral uptake?
By having an elongated shape and a large surface area in contact with soil particles.
What happens when plants lose too much water through transpiration?
They may wilt, as water loss exceeds the rate of water uptake by the roots.
How does evaporation from spongy mesophyll cells affect water movement?
It creates a pull that drives the transpiration stream, facilitating water movement from roots to leaves.
What is the primary role of root hair cells in plant nutrition?
To absorb water and dissolved minerals from the soil efficiently.
How does a plant regulate water and ion entry into the xylem?
By using selectively permeable membranes in root cells.
Why does water move down a water potential gradient?
Water moves to regions of lower water potential to equalize the concentration of solutes.
How does soil composition affect water and mineral uptake?
The presence of ions and the water potential in soil influence the rate and efficiency of absorption.
What controls the entry and exit of materials in plant cells?
The cell membrane controls the entry and exit of materials in plant cells.
What happens to a plant cell in an environment with high water potential?
Water enters the cell by osmosis, making it turgid and providing support.
What is a turgid cell, and why is it important?
A turgid cell is swollen with water, and its internal pressure supports the plant.
What happens when a plant cell loses water?
It becomes flaccid, leading to wilting of the plant.
