Chapter 4: Transportation in Plants - Biology

Question 1

Diffusion

Answer 1

Net movement of particles from areas of higher concentration to areas of lower concentration until an equilibrium is reached

Question 2

Osmosis

Answer 2

It is the diffusion of water molecules across a membrane
* When water solution has high solute, the water concentration is low whereas when water solution has lower solute, water concentration is higher
* Diffusion and Osmosis occur naturally due to the random movement of particles
* Particles move down their gradient by diffusion, and Osmosis does not require energy to do so
* ACTIVE TRANSPORT: For sugar, and many other nutrients, in order to move across the membrane, energy is needed

Question 3

Transport in Xylem

Answer 3

• Vessles, and tracheids of the roots, stems, and leaves are interconnected forming a continuous system of water-conducting channels that reach all parts of the plants
• There is a steady movement of water into the root xylem causing a positive pressure that steadily pushes a colum of water upwards
• The pressure itself is unlikely to be enough for water to travel the heights of plants we commonly notice
• Plants use cohesion-tension model to move water in the xylem upwards to the highest points of the plant body

Question 4

Moving water through the systems

Answer 4

“The push from below”:
* Water enters the root by osmosis, and moves towards the center of the root into the xylem vessels
* The pericycle (a thin layer of plant tissue between the endodermis, and the phloem) prevents the water from moving backwards
* Root pressure builds in the xylem and pushes the water up

“The pull from above”:
* While the roots push the water column from below, the leaves pull from above
* Transpiration (exhalation/evaporation of water through the stomata) helps the process

Question 5

Transpirational Pull: Pulling water up against gravity

Answer 5

• Cohesion-Tension Model: it is responsible for for majority of the movement of water & minerals from the roots to the leaves even in the tallest trees
• Transpiration of water creates negative pressure which acts to pull the water up to replace the lost water

Question 6

3 major factors in cohesion-tension model

Answer 6

Transpiration: Evaporation of water molecules from the shoot system is the main reason for water molecules & dissolved minerals to move upward in a plant stem

Cohesion: Columns of water in the xylem contain the property. It is the ability of water molecules to cling to each other, holding the water column in the xylem together while it is being pulled up under tension

Adhesion: The ability of the water molecule to stick, or adhere to certain surfaces like the walls of a xylem vessel to fight the force of gravity, and keep it from breaking as it is pulled upwards, and also prevent it from falling back down the roots

Question 7

The movement of maple sap

Answer 7

• Need to nourish many buds that must divide, and grow leaves that can photosynthesize
• In spring, large amounts of sucrose is converted from starch, and goes upwards from the roots through the phloem of the maple trees to help produce leaf buds, and where else it is necessary
• Once leaves grow, they make their own glucose through photosynthesis
• In the summer, and fall, when the leaves produce more glucose than necessary for their cells, then the excess glucose is sent back to other plant tissues, or stored as starch in the roots

Question 8

Nutrient transport in Phloem

Answer 8

Translocation: Transport of sucrose, and other organic materials through the Phloem. Moves sugars throughout the plant to be used for metabolism, growth, and storage.

Pressue-Flow Model: Uses a combination of osmosis, and pressure dynamics to explain how materials are pushed from the source to a sink in translocation.