Warmup 11/10/15
Why is water important to plants?
Objective
To learn how plants function
with relation to water
Tonight’s Homework
pp 319: 2, 3, 4, 7
Notes on Plants and Water
It may seem obvious, but different kinds of
plants require different amounts of water.
A corn plant may require 50
gallons of water in a single
growing season.
A cactus, on the other hand,
may not see that much water
in 10 years.
Notes on Plants and Water
Plants are mostly water. If you could take 10
grams of grass and dry it, the result would only
weigh 3 grams. Based on all this information, we
can certainly conclude that water is important to
plants! So how do they use water?
Notes on Plants and Water
Plants are mostly water. If you could take 10
grams of grass and dry it, the result would only
weigh 3 grams. Based on all this information, we
can certainly conclude that water is important to
plants! So how do they use water?
- Photosynthesis. For each molecule of glucose,
a plant needs at least 6 molecules of water.
- Turgor. Water helps fill and stiffen plant cells,
providing support for the plant.
- Hydrolysis. Plants use water to break apart
other needed molecules.
- Translocation. Materials can’t move through
plants without water to help!
Notes on Plants and Water
Water in the Soil
Most plants cannot absorb water through their
leaves or stems, only the roots. As such, there
are a number of key factors about soil we need
to be aware of.
Notes on Plants and Water
Water in the Soil
Most plants cannot absorb water through their
leaves or stems, only the roots. As such, there
are a number of key factors about soil we need
to be aware of.
- Soil Texture: Particle size
is important in how much
water can be absorbed.
A proper mix of soil (or loam) is about 40%
sand, 40% silt, and 20% clay. Variations from
this can result in poor water absorption.
Notes on Plants and Water
- Topsoil: This is made of loam, living
creatures, and dead organic material. Living
organisms make up about 10% of the weight of
good soil. More than you’d expect!
Notes on Plants and Water
- Topsoil: This is made of loam, living
creatures, and dead organic material. Living
organisms make up about 10% of the weight of
good soil. More than you’d expect!
- Pore Spaces: All these factors determine the
size of the pore spaces in the soil. Pore spaces
are places in the soil where water can be
absorbed and held.
Smaller pore spaces absorb water slower but
hold it longer. Larger pore spaces absorb water
faster, but hold it for less time.
Notes on Plants and Water
- Submersion: What if we submerged a plant
fully in water? You would think this would help
the plant be healthier, but this isn’t true.
Like any other living thing, plants need oxygen
and carbon dioxide to survive. Only special
plants can survive with their roots completely
submerged.
Notes on Plants and Water
Roots can only one use kind of water in the soil.
This is capillary water, the water stored in
pore spaces. Any other kind of water in the soil
is unusable by plants because they can’t absorb
it into their roots.
Notes on Plants and Water
Water Absorption
Water is absorbed into the
roots by a form of
pressure.
As the leaves pull water
upwards, this creates a
bit of a vacuum lower
in the plant, like sucking
on a straw.
This leaves the roots dry and more than willing
to absorb more water (without using energy!)
Notes on Plants and Water
Translocation of Water
When minerals and water move through a plant,
we call it translocation. Most of this movement
is done through root pressure, but not all.
Plants sometimes have to resort to active
absorption to forcibly pull water upwards.
Notes on Plants and Water
Translocation of Water
When minerals and water move through a plant,
we call it translocation. Most of this movement
is done through root pressure, but not all.
Plants sometimes have to resort to active
absorption to forcibly pull water upwards.
They also use capillary action, (similar to a
paper towel soaking up water) to help pull water
higher.
All these methods combined bring water all the
way up a plant.
Notes on Plants and Water
We call this idea the transpiration-cohesion
theory, and it is based on 2 principles.
Notes on Plants and Water
We call this idea the transpiration-cohesion
theory, and it is based on 2 principles.
Transpiration – We said that the leaves pull
water up, but what happens when the leaves
are full? Transpiration is the process of water
evaporating from the leaves. This gives more
room for more water to be brought up.
Notes on Plants and Water
We call this idea the transpiration-cohesion
theory, and it is based on 2 principles.
Transpiration – We said that the leaves pull
water up, but what happens when the leaves
are full? Transpiration is the process of water
evaporating from the leaves. This gives more
room for more water to be brought up.
Cohesion – Water molecules stick together and
form thin films. This is why water will form into
round droplets and why small objects can float
on water.
Notes on Plants and Water
Turgor Pressure and Wilting
Plants use water to maintain turgor. This is
when a cell is bloated with water. In plants, this
is a good thing as it provides an extra store of
water and rigidity to the cells.
Notes on Plants and Water
Turgor Pressure and Wilting
Plants use water to maintain turgor. This is
when a cell is bloated with water. In plants, this
is a good thing as it provides an extra store of
water and rigidity to the cells.
When a plant loses water, it will experience
temporary wilting. The plant loses a bit of
structure, but suffers no permanent damage.
This can be corrected with additional water.
Notes on Plants and Water
Turgor Pressure and Wilting
Plants use water to maintain turgor. This is
when a cell is bloated with water. In plants, this
is a good thing as it provides an extra store of
water and rigidity to the cells.
When a plant loses water, it will experience
temporary wilting. The plant loses a bit of
structure, but suffers no permanent damage.
This can be corrected with additional water.
Permanent wilting occurs when tissues die or
decay from lack of water, permanently
damaging the plant.
Exit Question
Define transpiration
a) The size of the spaces between grains of soil
b) The pulling up of water through a plant
c) The evaporation of water from the leaves of a plant
d) The rigidness of a cell containing a lot of water
e) The absorption of water without using energy
f) None of the above