Transport In Plants – C3.4 How can such a large tree transport water from the ground up into its top branches? Without water the tree will die because water is a reactant in photosynthesis. We might guess it costs the tree a lot of energy!

We have already learned about a handful of processes which move water in a plant. Osmosis Diffusion Active Transport Transpiration We can now put all the pieces together to get a clearer picture of material movement in plants.

Cohesion and Adhesion Plants act as pumps to pump water from the roots to the leaves. Water has certain properties which help plants use water efficiently. Water molecules are attracted to each other - Cohesion Water is a polar molecule where a tiny positive charge is attracted to a tiny negative charge on another water molecule.

Cohesion and Adhesion Since water is polar, it attracts itself to molecules of other substances. Water molecules “stick” to other substances. This called -Adhesion. In a plant the water molecules would adhere to the walls of the xylem.

Root Pressure Plants actively transport minerals into the root cells. As a result, the root becomes hypertonic to its surroundings and water follows. The water moving into the roots creates root pressure. This can be tested by cutting a plant and seeing the water seep up into the cut of the stem

Transpiration Pull The evaporation of water through stomata and lenticels creates a tension or transpiration pull. This pull is primarily responsible for bringing water from the xylem into the ground tissue. Transpiration depends on temperature - high temps increase transpiration

What happens when you put a plant cell in salt water? Tonicity in Plants What happens when you put a plant cell in salt water? The effect is called plasmolysis. This is where the cell membrane is no longer pushing against the cell wall.

Movement of Sugar in Plants Sugar is produced in the leaves - the source Sugar must move in the plant to a place where it will be used or stored - the sink Draw the figure on page 321 and label The movement of materials in and out of the phloem is called the pressure-flow theory

Control Systems - C3.5 You can respond to the environment. When you smell a pizza and you are hungry - you follow your nose and chow down! What about plants? Can they respond to their environment? How do they know they know what direction their roots should go? How do plants grow up toward the light?

As humans, we can respond to stimuli in our environment. A stimuli is a change in the environment which creates a response within an organism.

Phototropism Plants need to carry out photosynthesis to survive. In order for plants to be successful, they must be efficient at gathering the materials necessary for photosynthesis. Plants will grow toward the light - phototropism. Stems show positive phototropism because they follow light Roots show negative phototropism because they grow away from the light

Gravitropism Plants also respond to another stimulus gravity. Gravity effects plant growth and is called gravitropism. Stems show negative gravitropism Roots show positive gravitropism

Plant Response to Stimuli Plants that have roots growing away from light and that follow gravity are more likely to find minerals and water. Plants that have stems grow toward the light and against gravity are more likely to receive the solar energy needed for photosynthesis. “Tropism's” are important control systems which guide a plant reaction to certain stimuli.

Investigating Phototropism In 1880, Charles Darwin and his son Francis asked the question: What part of the plant detects and responds to the phototropic stimulus? They hypothesized that cells in the tip of a seedling were communicating with cells in the stem that bent a plant toward the light They tested this with a simple experiment laid out on page 327.

Investigating Phototropism In 1913, Peter Boysen-Jensen investigated how the tip and the seedling communicated. The area of the plant which bends toward the light was called the area of elongation because the cells on the “dark side” of the stem became longer causing the bend. Boysen-Jensen snipped off the tip of the seedling and paint gelatin on the end, then put the tip on - the seedling followed the light He then snipped the tip and placed a piece of thin mineral called mica in-between the tip and the seedling - no phototropism was observed Peter Boysen-Jensen hypothesized that whatever was responsible for communicating between the tip and the seedling must be able to diffuse through gelatin but not mica.

Investigating Phototropism Darwins Experiment

Investigating Phototropism In 1926, F.W. Went isolated the substance that was responsible for communication of phototropism responses. The substance was called auxin, a hormone which is produced in a plant and then transported to cells which elongate upon its contact.

Mechanism of Gravitropism Scientist believe that plants rely on heavy starch particles as an indicator of gravity If a plant is knocked over – the starch grains shift and settle in a new location After movement is detected, then a growth response results

Other Control Mechanisms Pea plants – Climb on a chain link fence Poinsettias – need longer nights to flower (Christmas flower)

HOMEWORK Read pages 315 -328 Do worksheet C3.4- Transport in plants Do worksheet C3.5 – Control Systems Prepare for Section C3.0 Quiz Do Section 3 Review – p.330 #2,3,7,9,10,12,14,16,17-20, 22,23,25 Prepare for Biology Vocabulary Quiz

Homework Prepare for Unit Exam Do Unit Review – p. 334-335 #’s 2-5,7-11, 13-15, 17-25