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How plants work

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Cjay R

on 4 June 2014

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Transcript of How plants work

The Stem
Root Structure and Function
How plants work
Anchor the plant in the ground

Absorb water

Absorb nutrients by drinking them in with water

Store sugars (sometimes)

Feed microbial life in the soil
What roots do for the ecosystem

To break down rock into smaller pieces, creating the inorganic part of soil

To prevent or reduce runoff and erosion, maintaining healthy and fertile topsoil.
There are two main kinds of roots
Taproots reach much deeper in the ground, good for getting water and nutrients that aren't available frequently on the surface.
Trees, carrots and dandelions have taproots.
Corn. wheat, and most grasses have fibrous roots.
Fiberous roots can absorb water and nutrients more quickly- but also need more frequent rain and fertilization.
Some plants grow roots in the air that reach to the ground- called adventitious roots
Tubers - delicious, delicious roots
Tubers are plants that store sugars underground. Potatoes, sweet potatoes and Taro are examples.
What do plants absorb from the roots?
Primary nutrients, (NPK)

Secondary nutrients (Ca Mg, S)

B Cu Fe Cl Mn Mo Zn
How do plants drink?
Plants have to absorb water through the cell walls in their roots. To increase their surface area, roots grow root hairs.
Osmosis and transpiration
Roots feed soil life
Plants don't just store the sugars they make from photosynthesis. They give some out through their roots into the soil to encourage friendly bacteria and fungi to live nearby.
The many jobs of roots
Micro-organisms add nutrients to the soil and help the plant absorb more than it could alone.
Root tips are where growth occurs
Xylem up, Phloem down
Plants use special tissues to transport fluids-
moves water and soluble nutrients up the stem or trunk from the roots, and
brings sap (sugary water) down from the leaves to feed the rest of the plant.
Osmosis is a process where water moves from an area of high concentration of soluble particles across a membrane to an area of low concentration,
Osmosis is "passive transport" - the plant doesn't need to use any energy.
The water (and dissolved nutrients) pass through the cell wall, and through some more cells until it gets to the vascular tissue.
How do plants get water all the way to their leaves?
Water sticks to other molecules of water (
) and to other surfaces (
), This causes
capillary action
- where water climbs up narrow tubes. When water is lost from the top of the tree, it pulls more water up behind it. (
Transpiration is the water that evaporates from leaves. On hot and dry days, just like people, plants will lose a lot more water from evaporation.
Ever notice how if you put a straw in water, the water in the straw is higher than in the cup?
Lets follow the water up the stem!
What roots do for the plant
What goes on in the roots?
What does the stem do?
Root Pressure
Osmosis causes pressure in the roots. Water tries to enter the root if there is a lot of in the soil.

If plants get a lot of water at night when they aren't using it, the root pressure can push the water into the plant, up it's stem, and, if the plant is short, out of special channels in it's leaves!
If the xylem (that transports water up) gets an air bubble in it, adhesion (water sticking to water) can't be used to pull water up to the top of the plant.

That's why, if you cut flower stems under water, they will live longer- they won't get air bubbles in the xylem that stop them from pulling water up to the flower.
Extra Credit
That's called :
Holds up the plant, provides a framework for leaves, flowers, and seeds.

Transports water, nutrients and sugars.

If it's green- it will photosynthesize energy just like leaves.
The cells in plant stems are stiffer
The cells in the stem are specialized to be stiff, give the plant structure, and transport nutrients.
In large plants like trees, the older growth cells on the inside of the stem die off, and harden, providing strength to the rest of the tree.
In trees, a layer of growth tissue makes new xylem and phloem around the outside of the tree, underneath the bark. Only that part of the tree is alive.
Only the outside of tree trunks move nutrients and water
If you "girdle" a tree- cut all the way around the trunk, it won't be able to transport nutrients anymore, and will die.
Trees are dead in the middle
Delicious, delicious sap
The movement of sugars around in plants can be sweet for us. Phloem transports the carbohydrates made in photosynthesis up and down in plants.
Maple syrup is boiled down sap from the Maple tree. In the spring, when it is freezing and thawing, the tree moves sap back and forth from the roots where it is warm and the sap won't freeze up to the budding leaves and back. Tapping the tree at this time lets farmers collect the sweet sugary sap.
Stems (and roots) only grow from the tip, and in some cases, around the width of the stem
At the tip of each stem is where cell division occurs
Herbicides work in different ways, depending on how the plant absorbs and transports what it uptakes. Dandelions are dicots- there are poisons that can be sprayed to kill them but not grass, which is a monocot.
You can see how different the vascular system is in monocots and dicots
It's important to know the difference for how you care for the plant.
Not all plant stems are the same
Trees are Dicots- so their stems have a layer of meristematic (growth) tissue called the cambium that allows them to keep growing wider (secondary growth).
Not all stems can grow wider
Monocots are usually small herbaceous plants. They can only grow at the tips, and their vascular tissue is spread throughout the stem.
Some herbicides kill dicots and not monocots
Monocot vs. Dicot
The stem also puts out buds
Merisetms are root and shoot tips, and the cambium in trees and other dicots has meristematic (cell reproducing) tissue.
Stems hold up leaves, other stems...
and flowers
Types of Stems
Some parts that grow underground are technically stems- like tubers, bulbs, corms and rhizomes.
Stolons are runners that the plant sends out that make new roots and new plants.
Twining stem parts wrap around things they touch to help the plant climb.
Functions of Leaves
Manufacture foods (photosynthesis)

Exchange gasses through stomata

Evaporate water

Store nutrients

Leaf Structure
Leaves are usually only a few cells thick.
They have a dermis- a waxy layer of "skin" that protects them from evaporation and damage.
are the pores that open and close and allow gasses into and out of the leaf.

Two "
guard cells
" cause the stomata to open or close when they become turgid (filled with water), or lose water
When plants pump Sodium and Calcium ions into guard cells, it causes water to fill them due to osmosis, opening the stomata.
Transpiration pulls water up from the roots.
The opening of the stomata allows water to evaporate, which pulls more water up the stem from the roots.
Photosynthesis happens in the leaves
When the stomata open, it allows CO2 gas inside, allowing photosynthesis to start.

Plants look green because chlorophyll doesn't absorb green light
Chlorophyll absorbs red and blue light and reflects green, making plants appear green
When leaves lose their color in fall seasons, it's because there isn't enough light to phytosynthesize anymore.
Chloroplasts (the green) die off, first and the other colors that were already there become visible.
Leaves "breathe" out up to 90% of the water that's drawn up from the ground
On a hot and dry day, plants can lose a lot of water to evaporation. When it's windy, plants close the stomata to prevent excess evaporation.
On humid days, because there is so much water in the air, less water will evaporate.
Trees making "rain"
In a rainforest, or cloud forest, clouds and mist are formed from the trees evaporating water.

Large trees can transpire more than 100 gallons of water a day.

All that water vapor makes the forest cooler than open areas at the same elevation.
Trees affect their ecosystem because of all the water they put out into the environment.
Not only by providing shade, but by pulling up water from the ground and releasing it to their ecosystem, trees make possible for many other plants to live in the understory that couldn't otherwise live without them.
Photosynthesis uses CO2, water and light to create sugars for the plant. Lucky us, the waste products are Oxygen and water.
Tree roots can reach much deeper for water.
When leaves aren't green anymore
Root or stem?
Onions, potatoes, ginger, taro... There are lots of plants that have edible parts that are sometimes called roots and sometimes called stems. In the field, it's ok to call them either.
A leaf that isn't a leaf
When seedlings first come up, the first two leaves to come up aren't leaves, they are called cotyledons.
Cotyledons start photosynthesis, but unlike normal leaves they store nutrition from the seed while the plant is still developing.
There are so many kinds of leaves!!
Reproduction in plants
There are two ways plants can reproduce:

Asexually - by themselves, by copying themselves.

Sexually - where
they share genetic
information with
other plants.
The more evolved plants get, the more likely they are to reproduce by sharing genes with other plants.
Sexual reproduction gives diversity to the gene pool, so plants are more likely to have adaptations that make them healthier and more able to survive.
The oldest plants reproduce aesxually, sending out spores with their genes.
Flowers are an evolutionary adaptation
Almost all of the plants we eat flower and seed to reproduce.
Vegetables, grasses, even grains all produce flowers.
Pollination- by wind or by bee
There are actually many types of insects, including bees, flies, beetles, and butterflies that pollinate different plants.
Many plants have special relationships with their pollinators
90% of Flowers have both male and female parts
The new fruit may be the same or very different than the parent plant.
After a flower is pollinated- (and only after a flower is pollinated) fruit is formed.
All kinds of fruits!
Many fruits serve as a method of transporting the seed to another place it can grow.
If you were a plant, how might you convince animals to transport your seed to spread and grow other places?
Make a delicious treat for them to eat.
Animals transport... and deposit...
Fruits that aren't fruit
The majority of our food comes from flowering plants that are pollinated by bees.
Some of our foods are in danger!
Many pollinators are dying, and with them the species that rely on that individual insect to help them reproduce.
The bees need our help
Honeybees are facing colony collapse disorder and many beekeepers lose half of their hives every year.
Reduce pesticides
In Europe and other countries, it's known that colony collapse is due to the use of certain types of (neonicitinoid) pesticides and other
sprayed on
plants to
kill pests.
Save the soil to save ourselves
For flavorful and nutritious food, it's important to have both macro and micro-nutrients in the soil. Whether using chemical or organic fertilizer- building healthy soil produces tastier fruit.
Fruits may not be delicious if they are grown in poor soil
Flavor comes from nutrition. Plants get nutrients from the soil. To have flavorful food is to have healthy food- that comes from healthy soil.
Food needs to be harvested when it's ripe
They end up having less flavor and nutrition than when picked fresh. Then food tastes bland or needs chemical flavors to make up for the loss of taste, or sugar to make up for the loss of sweetness.
Some plants we grow for the leaves
Careful- if there are toxins in the soil, plants may absorb them and store them in the leaves.
Disease and nutrient deficiency ID
Leaves are a great way to identify problems with plants such as diseases or nutrient deficiencies.
The first true leaves
After the Cotyledons come up, the first true leaves will appear. These will start to have the characteristic shape of the plant species.
Chlorophyll is good for you!
Sometimes flowers pollinate themselves- but that doesn't give them the advantage sharing genes with another plant does.
Some plants do GREAT when pollinated by the wind. Grasses, for example, and plants that grow by the thousands in one area.
Others, not so much...
Most of our flowering food crops do really poorly with wind pollination. A lot of wild crops also depend on pollinators.
Honeybees may be what we first think of when we think of pollination
Honeybees pollinate most of our food crops- so that's a fair thought. In fact we would have only 1/3 of the foods we eat if it weren't for honeybees.
Are they the only pollinators?
Of course there
are butterflies
And hummingbirds
... that is if they are "dicots" (di meaning two) Monocots like grasses just send up one shoot.
If there is any chance of heavy metals in the soil where you are planting your vegetables, test the soil before you grow.
Sometimes they don't look like the flowers we first think of.
Colorful flowers attract pollinators
If some plants have plain looking flowers, that's because they are pollinated by the wind, and don't need to attract bees, flies or birds to pollinate them.
A tomato plant with flowers
A recently pollinated cucumber flower with cucumber growing
Flowers are an evolutionary adaptation
The stamen with the anther on top is the male part that releases pollen. The pistil is the female part that receives pollen.
Fruit is next
Once pollination occurs, the plant has the genetic material it needs to make fruit- it's way of reproducing.
Propagation from cuttings
So mosses reproduce asexually, and plants that flower and seed produce sexually.
Many plants can also grow from pieces of a parent plant. In the wild, this means when a piece of a plant breaks off it grows a new one. For human propagation, it means taking a cutting.
By reproducing sexually, plants have a broader gene pool and a better chance to survive.
Apple seeds are never the same as the parent plant. Many are inedible.
Birds transport... and deposit...
Fruits and some vegetables are harvested early so they can be transported long distances.
If picked now, this strawberry will last longer for shipment and on a shelf.
Only this one will ever taste sweet!
There are so many ways to adapt to an environment...
Cuttings will be genetically identical to parent plants.
Plants release pollen, are fertilized, make fruit, the seed grows a new plant with a new flower and....
If we didnt' have bees, there would be very little food at the grocery store.
More simply- Dicots, like trees, can keep growing wider.
Grass is a good example of a monocot.
Some plants like squashes, cucumbers and grapes have separate male and female flowers. Only the female plants will bear fruit.
Many plants protect against self-pollination by having their sexual parts mature at different times.
In a few species, male and female plants are separate.
Fig trees are one example.
Vegetables, and many other things that aren't sweet fruits are still the "fruits" of a plant.
That's right- fruits are ovaries.
the seeds are usually a much smaller part within the ovary.
Seeds are usually a small thing inside the fruit- or the ovary.
Even grains were once pollinated flowers
The wheat we eat in bread is a seed with a starchy area to feed the germinating plant, and a fibrous sheath to cover and protect it.
Good thing plants make fruits...
All we would have to eat without them are grasses and animals that eat grasses.
But why do plants make fruit? Why not just make seeds?
Fruits have different chemical (nutritional) properties when ripe and un-ripe.
If harvested too late- fruits will be "over-ripe"
Some vegetables will start to taste woody or bitter. Others may start to rot. Fruits will start to ferment.
Congrats on the giant zucchini... too bad it won't taste very good.
Plants bend towards the sun by elongating one side of their stem at a time.
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