lesson 7- part 1: specialized and organized

Specialized and Organized (the Leaf)

• How does a plant, a multicellular organism, obtain food, water, and minerals?

• How does it respond to its environment?

• What structures allow the plant to perform these activities?

• How are these structures organized and how do they function?

Cell Specialization in Leaves:

• The Leaves of all plants perform a crucial function for the Plant: PHOTOSYNTHESIS

  ("Photo" Light, "Synthesis"= To Put Together)

  H2O+ CO2 + light energy -> C6H12O6 + O2

• Photosynthesis converts Light Energy into Chemical energy in the form of Glucose (A simple Carbohydrate)

• At the same time Carbon Dioxide and Water are used up while Oxygen is produced

• Photosynthesis occurs in the Chloroplasts of the Cells found in Leave's of plants

• In order for a leaf to function at its best it has different types of cells within it that perform specific tasks for the leaf and therefore the whole plant

Epidermal Tissue Cells:

• ("Epi" = Over/On, "Derma" - Skin) Top and Bottom layers of a leaf Flattened cells

• Create a one-cell-thick protective layer for the leaf Covered by a waxy cuticle (less water loss) Contain no Chloroplasts and are transparent to allow light to pass through

Palisade Tissue Cells:

• Found just beneath the Epidermal Cells Long and narrow cells (column-like)

• Tightly packed layer

• Main type of Photosynthetic cells in leaf exchange

• Packed with Chloroplasts

Spongy Tissue Cells:

• Layers of cells just beneath the Palisade Cells

• Round shape

• Very loosely packed with many air spaces between them

• Also contain Chloroplasts to carry out photosynthesis

• Structure allows gas and water exchange with the outside environment

Stomata and Guard Cells:

• Allow Carbon Dioxide to enter the underside of the leaf Allow Oxygen and Water Vapour to exit the underside of the leaf

• Surrounded by two guard cells that regulate how the Stomata open and close

Vascular Tissue Cells:

• Form a series of tubes that allow Water and Sugars to be

• transported into and out of the leaf Visible as Veins in a leaf

• Made up of Xylem and Phloem Tissues

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

• Phloem carries sugars from the leaves to the rest of the plant

Cell, Tissue, Organ, System, Organism:

• A multicellular organism has many advantages compared with single-celled organisms:

• A larger size

• A variety of specialized cells

• An ability to thrive in a broader range of environments

• However this means that a multicellular organism needs organization

-Atoms -Molecules -Organelles -Cells -Tissues -Organs -Organ Systems -Organisms

Lesson 7- part 2: Gas exchange in plants

Gas exchange in plants: something in the air

Air is made of a mixture of:

• Oxygen

• Carbon Dioxide

• Water Vapour

• Nitrogen

• Other Gases

• Photosynthesis requires Carbon Dioxide which is taken into a Leaf through the Stomata

• Photosynthesis produces Oxygen that is released out of the Leaf through the Stomata along with Water Vapour

Leaves and Lenticels

• Leaves are the main area for gas exchange in a plant

1. Carbon Dioxide diffuses into a leaf through Stomata

2. Carbon Dioxide circulates in the spaces between the Spongy and Palisade tissues cells

3. Carbon Dioxide diffuses into the Spongy and Palisade Tissue Cells down a concentration gradient

4. Chloroplasts in the Tissue Cells undergo Photosynthesis, converting the Carbon Dioxide into Glucose and Oxygen

5. The plant stores the Glucose for use later

6. The Oxygen and Water Vapour diffuse out of the Tissue cells, into the spaces between the Spongy and Palisade Tissue Cells and finally out of the leaf through the Stomata

   Leaves and Lenticels

• Some gas exchange can occur throughout the rest of the plant

• However, in woody plants (Ex. Trees) gas exchange is difficult

• Woody plants contain Lens-Shaped openings called Lenticels that allow for gas exchange in their stem/trunk

Gas Exchange is Tied to Water Loss

Transpiration:

• Spongy and Palisade Tissues are surrounded by a thin layer of water

• The water will evaporate out of the leaf through the stomata along with Oxygen and other gases

• This loss of water is called Transpiration

• Transpiration can account for the loss of 99% of the water absorbed by the roots of the plant.

Stomata/Guard Cells

• Stomata help the plant from drying out

• When the stomata are open they allow for lots of gas exchange and transpiration

• This gas exchange and transpiration allows for a high rate of Photosynthesis

• However, when closed, gas exchange, Transpiration and Photosynthesis decrease

• Most often Stomata are open during the day and closed at night

Turgor Pressure

• The opening and closing of Stomata is also linked to Turgor Pressure

• Turgor Pressure is caused by the movement of water into the Central Vacuole of a plant cell.

• The Vacuole swells and pushes against the Cell Wall causing the plant cell to become swollen and more rigid

• Water will move into the Guard Cells of the Stomata through Osmosis causing them to swell and gain Turgor Pressure

• As the Turgor Pressure increases the Guard cells swell and stomata.

• As the water transpires out of the Guard Cells they lose Turgor Pressure, deflate and then the Stomata Close

Plant Adaptations

• Desert plants will open their Stomata at night (not during the day) to conserve water. Carbon dioxide is taken in at night and stored as a different chemical until it is used for Photosynthesis later in the day.

Lesson 8: water transport in plants

Xylem Vessels and Phloem Vessels

• Plants need a way to transport materials such as Water, Sugars and Dissolved Minerals throughout there various tissues

• In order to accomplish this task they contain specialized vascular tissues called the Xylem and Phloem

Xylem

• Transports Water and dissolved minerals from the soil to the leaves

• Xylem cells are dead at maturity and act like pipes within the plant

• The cells are linked to each other forming continuous tubes called Xylem Vessels

• Xylem Vessels can be divided into two groups:

1. Tracheid’s

2. vessel elements

• Water transport in Xylem Vessels allows for Photosynthesis and Turgor Pressure in plants

Phloem

• Transports Sugars produced by Photosynthesis from the Leaves to the rest of the plant

• Phloem cells are alive at maturity and also act as pipes within the plant

• However, Phloem cells are porous allowing the exchange of materials between the Phloem cells and neighbouring tissue cells

• The Phloem cells are linked to each other forming continuous tubes called Phloem Vessels (Note: Cells are separated from each other by Sieve Plates)

• Phloem Vessels can be divided into two groups:

1. Sieve Tubes

2. Companion Cells

• Sap transport in Phloem Vessels allows for nutrients to reach the various tissues in the plant

Water Uptake in Roots

• Water and minerals enter a plant from the Roots

• At the core of the root are the Xylem and Phloem

• Epidermal tissue covers the root

• At its tip, the epidermal cells are permeable to water and water enters the root here by osmosis

• Root hairs help to increase the surface area of the roots

• Water continues to diffuse into the root tissue until it reaches the xylem

• Although water diffuses easily across the cell membrane, minerals do not

• The plant must use Facilitated Diffusion or Active Transport to move minerals across the membrane

• The water and minerals that enter the Xylem is called the Xylem Sap

• The sap travels up through the Tracheid's and Vessel Elements of the Xylem Vessels towards the leaves As the Xylem sap enters the Leaves the Xylem Vessels branch into veins and deliver the water and minerals to the cells of the leaves

Properties of Water

• How does the Xylem Sap rise up to the top of the Plant?

• Water is a Polar Molecule and the negatively charged Oxygen of one water molecule will attract the positively charged Hydrogens of another water molecule

• This phenomenon is called Cohesion and it helps to drag the water up the Xylem Vessels

Cohesion:

• Cohesion allows water molecules to transport through the Xylem like a chain where each water molecule is a separate link in the chain

• If there is a bubble in the Xylem or the water freezes the Cohesion can be disrupted and only the water molecules above the break will continue upwards

Adhesion:

• Water also has the ability to attract to other molecules

• This attraction is called Adhesion and allows the water molecules to climb up the walls of the Xylem Vessels .

Transpiration Pulls

• Root Pressure, Cohesion and Adhesion will work for small plants but what about huge trees?

• Transpiration helps move the water up the xylem by evaporating water out of the leaves

• Since Water drags the water up from the roots as the water evaporates out of the leaves

Root Pressure Pushes

• Cohesion and Adhesion help to drag the water molecules up the Xylem Vessels of the plant, however, the roots also help to push the water up the plant

• Turgor Pressure within the roots helps to force the Xylem sap into and up the Xylem Vessels

• As Minerals are Actively Transported into the root it makes the root Hypertonic and thus brings in more water by osmosis adding more root pressure helping the Xylem Sap to move upwards

Sugar Transport in Phloem

• After Photosynthesis has occurred in the leaves the sugars must be transported to the rest of the plant to be used as energy

• Phloem transports the sugars (and other materials) throughout the plant

• As the Sugars enter the Phloem Vessels the solution becomes Hypertonic and draws in water by osmosis

• This solution is then called Phloem Sap and the Sap will move throughout the Phloem Vessels down a concentration gradient to the rest of the Plant tissues

Lesson 9: plant control systems

Plant Control Systems

• Animals have the ability to sense and then respond to their environment by thinking and acting

• Plants cannot think, however, they do Respond to their environment as well

• These responses to the environment are called Tropisms in plants

Phototropism

• The growth of a plant toward a light source

• Phototropism allows the plant to maximize the amount of light that is absorbed by the leaves which in turn maximizes the amount of Photosynthesis within the leaves

• Since the plant can not move, Phototropism is accomplished in an interesting way In order to bend towards the light a plant will have the cells of its stem grow at different rates

• Cells on the side of the stem that is further from the light will grow longer than the cells on the side of the stem that are closer to the light

The Darwin's' Experiment

• In 1880 Charles Darwin and his son Francis performed experiment to prove that plants will grow toward a light source

• In their experiment they not only proved that plants respond to a light source, they also proved that it was the tip of the plant that would sense, respond and then send

The Boysen-Jensen Experiment

• Decades after the Darwin's' Experiment a Danish scientist named Peter Boysen-Jensen continued on with Darwin's idea

• He was interested in the actual signal that was sent from the tip of the plant in response to light

• He cut the tip of a plant off and replaced it with both Gelatin and Mica

• The Gelatin-tipped plant grew toward the light as the signals were able to diffuse through it

• However, the signal could not diffuse through the Mica and the plant grew straight up and did not respond to the light proving that the signals are sent from the tip of the plant to the rest of it

Auxins: Plant Growth Chemicals

• Fritz Went's Avena Experiment:

• In 1926 a Dutch Scientist named Fritz Went confirmed the hypothesis that a growth chemical signal is produced in the plant tips and are sent to the rest of the plant

• He extracted the chemical by removing the tips from young stems and then placing the tips in Agar (a growth material)

• The chemical signal diffused into the Agar

• He then took the chemical filled Agar and put them onto the cut tips of small Oat seedlings

Fritz Went's Results:

• Went found that the plants grew in different ways! Plant tip Completely covered by chemical soaked Agar = Plant Grew Straight Up

• Plant tip Partially covered by chemical soaked Agar - Plant Grew Away from the Side with the Chemical Soaked Agar

• Plant tip Completely covered by Non-chemical soaked Agar - Plant Did Not Grow At All

• Went concluded that the chemical produced in the plant tips stimulated Growth

• This chemical was called Auxin (Greek for "To Grow")

Action of Auxins:

• Auxins are produced in the tip of the plant as it responds to a light source

• After Auxin is produced in the tip of the plant it travels to the shaded side of the stem

• Active transport moves the Auxin into the cells of the shaded side of the plant

• The Auxin then causes the cells on the shaded side of the plant to grow longer than those cells on the lighted side causing the plant to bend toward the light

Gravitropism

• Gravitropism is a plant growth response to Gravity (an environmental stimulus)

• Positive Gravitropism:

• Positive Gravitropism occurs in the Roots of plants which the roots will grow downwards with gravity

• Negative Gravitropism:

• Negative Gravitropism occurs in the Stems of plants in which the stem will grow upwards against gravity

Gravitropism and Auxin

• Gravitropism also relies on the ability of the plant signal Auxin to elongate the cells on one side of the stem or the roots

• This is accomplished in opposite ways in the Stem vs. The Roots

• Gravitropism in the Stem:

• A plant will respond to gravity by releasing Auxin from its tip (ex. If a plant was on its side)

• The Auxin will be sent to the lower side of the stem stimulating the cells on that side of the stem to elongate

• The stem will bend to grow upwards against gravity

• Gravitropism in the Roots:

• A root will respond to Auxin in the opposite way

• The Auxin will be sent to the lower side of the roots inhibiting the cells on that side of the root from elongating

• The roots will bend to grow downwards with gravity

Nastic Response

• Some plants have the ability to respond to Touch Ex. Venus's-Flytrap and the Mimosa Plant

Cells and Complex Responses in Plants

• Imagine how difficult it must have been for ancient scientists to solve the questions about life works without some of the modern technologies we take for granted today

• The invention of the microscope and the discovery of the cell has allowed modern scientists to explain and even predict observable events such as the closing of a Venus's-flytrap!

• These responses. Performed by many co-ordinated cells, combine to create a fantastic whole: a living, respiring, moving, multicellular organism/