Unit 8 Transport in Plants

- What is mass flow?

In large animals, the transport systems move fluids through tubes so that all the fluid moves in the same direction within each tube.

- What are the transport systems in plants called?

xylem and phloem

- Where are xylem and phloem found in the plant?

throughout the plant body in roots, stems and leaves

- What is the function of xylem?

xylem transports water and mineral ions, the water from the roots enters the xylem in the root and travels upwards in the stem to the leaves, flower and fruit, uni directional flow

- What is the function of phloem?

Phloem transports sucrose, amino acids and hormones throughout the plant, bi directional flow

- What is sucrose?

a soluble complex sugar that is made in the leaves with the sugars from photosynthesis and starch in storage organs to transport energy

- What do hormones do?

control cell division for growth of the stem, roots, flowers, fruits and leaves

- In a root, what is the function of root hairs?

to absorb water and mineral ions

- In a root, what is the function of the cortex?

stores some food as starch

- In a root, what is the structure of the root tip?

it grows as the cells divide

- In a root, what is the function of the root cap?

protects the root tip as it grows through the soil

- In a stem, what does the vascular bundle made up of?

phloem, xylem and cambium

- In a stem, what is the function of cambium?

making of new xylem and new phloem as the plant grows

- In a stem, what is the structure of the epidermis?

single layer of cells on the outside of the stem

- In a stem, what is the function of the epidermis?

protection of the stem and reduces the water loss

- What is the function of the roots?

to anchor the plant in the soil and take up water and mineral ions

- How does water pass into the root hairs from the soil?

through osmosis⇒ the root hairs have thin permeable cell walls that provide a large surface area to absorb water. The water diffuses into the root hair through its partially permeable cell wall. The root hair cells have a more concentrated solution than soil water because they have solutes like sugar and also absorb mineral ions.

- Describe the movement of water into a root hair, across the cortex and into the xylem vessel in terms of water potential?

Water passes down a water potential gradient from a high water potential in the solution in the soil to a lower water potential in the root hair cell, water passes further through the cortex and xylem vessel in an even lower water potential.

- How are root hair cells adapted for the absorption of water?

they have thin cell walls and a large surface area

\-Transpiration

loss of water vapour from the leaves

how does the size and number of the stomata affect the rate of water loss by transpiration

more water is lost because the large air spaces would provide a larger surface area for evaporation of water

why is stomata open during he day and closed at night?

open during the day so that co2 can diffuse into the leaf for photosynthesis, the stomata is closed at night to reduce the volume of water lost by transpiration

why do the stomata close in hot, dry conditions?

to reduce the amount of water lost in transpiration as it is not being replaced by the soil

what happens to the plant when it doesn’t get enough water?

it starts to wilt

what happens to the plant when it wilts?

the plant has lost a lot of water, so its cells are no longer turgid, firm and full of water, turgid cells give the plant support, without it stem doesn’t stay upright and its leaves drop.

how does wilting help the plant?

the leaves move downwards and stay out of direct sunlight so they don’t get hot, when the temperature decreases the plant goes back to normal

transpiration stream

movement of water up the xylem

xylem vessels

long, continous columns of cells in the xylemn

what is lignin and how does it help the plant?

impermeable, woody material which strengthens the mechanical strength of the xylem vessels and helps it withstand the strong pressure that occurs during water transport, nothing can pass through the xylem cells, the xylem vessels are hollow

Transpiration pull

movement of water up the xylem vessels in a stem from the roots to the leaves

Cohesion

water molecules attract each other, stick together and move upwards together

adhesion

water molecules stick together inside the xylem vessel which reduces the chance of the columns of water being broken

with what do you measure the rate of water uptake?

a potometer

what are the 4 factors of transpiration?

1. light
2. temperature
3. wind speed
4. humid

how does light affect transpiration?

when there is more light, the stomata opens allowing more water to be lost by transpiration, when there is less light the stomata closes so less water is lost by transpiration

How does temperature affect transpiration?

rate of transpiration increases as temperature increases because the kinetic energy of the water molecules increases

How does wind speed affect transpiration?

the rate of transpiration increases as the wind speed increases because more water is blown away from the stomata by net diffusion

how does humidity affect transpiration?

more humidity decreases the rate of transpiration because the water vapour in the atmosphere is the same as the water in the stomata so there is no concentration gradient

what do leaf cells convert glucose to for transport?

sucrose

How do leaves make amino acids?

using glucose and nitrate ions

what happens to sucrose and amino acids in translocation?

Sucrose and amino acids are taken to organs where they are used in synthesis or where sugar is respired to provide energy for growth

How does glucose help the plant?

1. broken down in respiration to provide energy
2. built into starch for storage in roots and seeds
3. built into cellulose for new cell walls at root tips or shoot tips
4. stored in the stem of some plants
5. and in some fruits to make them sweet to attract animals
6. used to make nectar to attract pollinators

How does the movement of the phloem work?

requires active transport of sucrose, the sucrose lowers the water potential in the phloem tubes so that water enters by osmosis

How do aphids get food from the phloem tube?

they insert their mouths (stylets) onto the surface of the stem into a single phloem tube, the pressure of the sap inside the tube causes it to pass the sap to the aphid

How do you study the transport of sugars using aphids?

you cut the stylet of a feeding aphid, and a sugary sap will pass out of it

how is maple syrup prepared?

farmers drill holes into trees and insert tubes through which the sap flows and collects into a bucket