Chapter 9

From cell to Organism : Plants

Overview: Organization of the plant cell Exchange of gases Water transport Plant Control Systems

9.1 – Specialized and Organized

In single celled organisms, one cell must be able to perform all the functions of like.

In multi-cellular organisms, many cells work together to meet the needs of the organism. Group of specialized cells perform specific tasks.

Cell Specialization in Leaves

Leaves contain several types of specialized cells that help with photosynthesis

Chemical process where carbon dioxide and water form glucose and oxygen

6H2O + 6CO2 ----------> C6H12O6+ 6O2

Epidermal Cells

Protective layer covers the plant’s leaf Forms the epidermis Covers the upper and lower surfaces of the

leaf A waxy substance (cuticle) coats the cells to

prevent evaporation of water from the leaf Do not have chloroplasts

Palisade Tissue Cells

One of the main types of photosynthetic cells Long and narrow like columns and are

packed closely together Shape and organization make photosynthesis

within the cells efficient Upper surface of the leave and contain

chloroplasts

Spongy Tissues Cells

Contain chloroplasts and carry out photosynthesis

Layered below the palisade tissue cells Round and loosely packed and have many air

spaces between them Structure helps the cells to exchange gases

and water with the environment

Stomata and Guard Cells

Stomata - Small opening in the epidermal later to allow gases in and out of the leaf

Guard cells – are near the stomata to control the size of it. Can change shape to open or close the

stomata

Vascular Tissue Cells

Two times of tissues are called xylem and phloem

Xylem – carries water and minerals from the roots to the leaves

Phloem – carries sugars produced by the leaves to various parts of the plant.

The tissues are arranged together in vascular bundles

Cell, Tissue, Organ, System

Multi-cellular organisms can have: A larger size A variety of specialized cells An ability to thrive in a broader range of

environment

In Multi-cellular organisms, groups of specialized cells are organized so that they can perform their functions efficiently

Cells are the most basic level of organization, while systems are the most complex.

Cells- most basic unit of organization in organisms

Tissues – cells that are similar to each other are often clustered together

Organs - can be formed by combining multiple tissues

Systems- organs can function together at an even higher level of organization Organs and tissues throughout the body perform

a shared complex function

Page 324 Questions 1 & 7

9.2 Gas Exchange

The stomata in the outer tissues of the plant’s leaves allow gases to diffuse in and out of the leaf

Inside the leaf, there are spaces between some of the cells that allow gases to move in and out freely

Something in the Air

During photosynthesis, plants consume carbon dioxide and water to produce oxygen.

Leaves and Lenticels

The most important gas-exchange organ in the plant is the leaf.

Air diffuses through the stomata and into the leaf.

It circulates in the spaces between the spongy and palisade tissue cells.

Carbon dioxide diffuses down its concentration gradient.

Oxygen produced during photosynthesis passes out of the cells and into the air spaces.

Then oxygen will go to the stomata and out of the plant.

In the roots and stem, some gas exchange occurs.

In woody plants, the layer of dead cork and waxy substances prevent this.

In these plants, lens-shaped opening called lenticels perforate the bark of these plants.

Gas exchange is tied to water loss.

Palisade and spongy tissue cells are coated with a thin layer of water

As the air diffuses out of the stomata, some water is lost.

The evaportation of water from leaves is called transpiration. This can lead to 99% of water absorbed by the

root.

To keep the plant from drying, the guard cells can change their shape to cause the stomata to open or close.

The size of the stomata controls the amount o gas exchange and transpiration.

High rates of photosynthesis are possible when the stomata are open.

When the stomata is closed, gas exchange and water exchange are reduced.

Water moves in and out of the cell through Osmosis.

As water moves into the guard cells, the water pressure inside the cells increases and causes the cells to swell.

The high water pressure is called turgor pressure.

Turgor Pressure pushes the elastic cell membrane against the rigid cell wall.

The swollen guard cells change shape, opening the stoma.

This will cause transpiration to make the plant cell balanced.

In most plants, the stomata is open during the day and closed at night.

Plants though who adapt to extremely dry condition have their stomata only open at night.

In the desert, plants store carbon dioxide to perform photosynthesis during the day.

Plants can still dry out though The plant’s leaves droop and wither, and the

stem softens and bends. Like the guard cells, other cells throughout the

plant have reduced turgor pressure as a result of water loss.

If they are supplied with more water, the limp cells have their turgor pressure restored, which renews their shape and rigidity.

Questions 1- 5

Due Friday November 4th 2010

9.3 Water Transport in Plants

Some trees are more than 100M from root to tip.

We are going to investigate the transport of water and nutrients in the plant vascular system.

You will identify the cells, tissues and organs that make up this system.

Xylem Vessels and Phloem Vessels

Like our circulatory system that carries blood, plants vascular system is made up of interconnected tubes.

Xylem and phloem are specialized tissues that make up this system of transport. They are found in the roots and stems of the

plant as well at the leaves

Xylem tissue transports water and dissolved minerals from the soil to the leaves.

In mature plants, most xylem cells are dead, as they form hollow tubes consisting of only the cell walls.

The cells are linked end to end, forming long continuous tubes called xylem vessels. These extend from near the tips of the roots

up into the rest of the plant

Some sugars produced during photosynthesis are transported throughout the plant by cells of phloem tissues.

The phloem is composed of cylindrical cells joined end to end to form phloem vessels.

Phloem cells are living and their cell walls are porous allowing them to exchange materials.

Sugary sap flows down the phloem vessels by passing through these pores.

The Long hollow cells within xylem vessels are called Tracheids or Vessel elements.

Some types of plants have both but some only have tracheids

Both begin as living cells until the plant is mature then the cells die off

Fluids pass from one tracheid or vessel element to the next within the xylem to move water.

Phloem cells consist of sieve tubes and companion cells arranged end to end.

These cells connect in long tubes, separated by sieve plates, to make the phloem vessels.

Water Uptake in Roots

Water and minerals enter a plant from the roots.

At the core of the root there are the xylem and phloem encircled by several other layers of cells Epidermal tissues which is where the water

enters the plant by osmosis.

The surface area for absorbing water and dissolving minerals from the soil is increased by hundreds of root hairs.

Each hair is an out growth of a single epidermal cell.

Minerals do not readily diffuse across the cell membranes

Roots cells use facilitated diffusion or active transport if against the concentration gradient

Solution of water and minerals that accumulates in the root xylem is called xylem sap

Xylem vessels carry the sap upward from the roots through the stem then into the leaves

Properties of Water

The shape of water molecules and the weak electrical forces between them, cause water molecules to be attracted to each other.

Cohesion, the tendency of water molecules to stick to other water molecules, transmits the upward pull from the tip of the leaves to the tip of the root.

Another property of water is adhesion The tendency of water molecules to

stick or adhere to certain surfacesJust as water will attract to one

another, they will attract to molecules of other substances such as the cellulose wall of a xylem vessel.

Root Pressure Pushes

In the roots, one force that pushes fluid upward is turgor pressure inside the root xylem.

This is called root pressureThe root cells bring minerals into the

xylem through active transport.This increases the tendency of water to

diffuse into the root xylem by osmosis.

The pressure from this, will force fluid up the xylem.

Adhesion of the xylem sap to the xylem vessel walls help the fluid climb upward.

Transpiration Pulls

Because the pressure changes at you get higher on a 100m plant, some other factor has to help bring the water to the top of the tree.

Transpiration from the leaves generates this pulling force or tension.

When water is evaporated, it causes the solutes to be more concentrated.

Osmosis must occur in order to restore balance.

Sugar Transport in Phloem

After water and minerals enter the leave, the plant can carry out photosynthesis.

The sugars are produced by the palisade tissue cells and spongy tissue cells provide energy for the entire plant.

As the sugar concentration increases, water follows the sugar by osmosis.

The cells swell with the increase in turgor pressure

The sugar, nutrient, and water mixture called phloem sap, flows down the concentration gradient.

The phloem vessels transport the sugars and other substances throughout the plant.

Sugar, minerals and other nutrients are pumped into the leaf phloem by active transport

9.4 Plant Control Systems

Stimuli – an environmental factor that an organism is responding to.

Phototropism – the growth of a plant toward a light source This maximizes the amount of light absorbed

by the plant’s leaves Plants do this by having there cells grow at

different rates This will cause one side of the plant to be

elongated more than the other side.

Auxins: Plant Growth Chemicals