Plant physiology (copy)

What are the two types of vessels within vascular bundles?

Xylem and phloem

What does overfertilization of soil do?

Increases osmotic concentration (increases salt concentration in the soil), which drains water from the plant

Plant wilts and dies

What is the pulling force that brings water and dissolved minerals up from the roots?

A tension force generated by transpiration

How does transpiration work?

The evaporation of water from leaves through open stomata

The loss of water by transpiration causes water to be pulled through the cell walls of nearby xylem tissue by capillary action

What is cohesion-tension theory?

Tension results in the movement of water up the xylem, and the entire column of water moves up because of cohesion

How are xylem tubes formed?

When alive, cylinder-shaped plant cells have complete cell walls, plasma membranes, and organelles

When cells die, they leave behind only thick cylinder-shaped cell walls

End walls where the cell were joined to each other in the tube completely or partially degenerate

What is lignin?

Organic polymer that provides resistance to the collapse of the tubes because of the tension created by transpiration

Why are there small pits (microscopic holes) in the sidewalls of the xylem?

Allows easy flow of water in and out of the xylem vessel as needed

What are the five dicotyledonous stem tissues?

Epidermis

Cortex

Xylem

Vascular bundle

Phloem

What is the function of epidermis?

Prevents water loss and provides protection from microorganisms

What is the function of the cortex?

An unspecialized cell layer that sometimes stores food reserves

What is the function of xylem?

Transport tubes that bring water up from the roots

What is the function of phloem?

Transports carbohydrates, usually from leaves to other parts of the plant

What is the function of a vascular bundle?

Contains multiple vessels of both xylem and phloem

What is the structure of tissues in a dicotyledonous root?

What is the function of the epidermis in a dicotyledonous root?

Grows root hairs that increase the surface area for water reuptake

What is the function of the cortex in a dicotyledonous root?

An unspecialized cell layer that stores food reserves

What is the function of the xylem in a dicotyledonous root?

Transport tubes for water and minerals, starting in the roots

What is the function of the phloem in a dicotyledonous root?

Transport tubes that receive sugars from leaves

What is the function of a vascular bundle in a dicotyledonous root?

The area in the centre of the root containing xylem and phloem

Do plants cease water movement in xylem when transpiration is not possible (ex. when stomata are closed or leaves are not present)?

No, plants are able to move water into their roots and up the xylem even in the spring, when leaves on deciduous plants have not yet grown

Also in highly humid situations where transpiration is not possible

What is a deciduous plant?

Loses its leaves seasonally, typically in autumn in temperate climates.

How do root cells create a low water potential? What does this allow for?

Active transport of mineral ions into cells

Root hairs will take in water by osmosis in this manner

Describe transport of mineral ions to xylem tubes in the centre of the root.

Mineral ions can diffuse or be actively transported across the epidermis and cortex of the root until the minerals reach the xylem tubes in the centre of the root

What tissues do water and dissolved minerals need to pass through to get to the xylem?

Epidermis, cortex, and then the xylem in the central part of the root

How do mineral ions relate to water transport?

Water always follows solutes by osmosis, as the presence of mineral ions creates an area of low water potential

This not only allows water to enter the xylem but also creates a positive fluid pressure pushing the column of water upwards

Why do plants require water?

Light-dependent part of photosynthesis runs on electrons and protons extracted from broken water molecules in water photolysis

Why are leaves thin and composed of only a few cell layers?

Permits a relatively large surface area to volume ratio for efficient diffusion

What are the two primary energy-related processes within plants?

Aerobic cell respiration to synthesize ATP for energy-requiring reactions

When light is available, plants use photosynthesis to make sugars as fuel for cell respiration

Are the rates of cellular respiration and photosynthesis equal?

No. The rate of cellular respiration is fairly constant, while the rate of photosynthesis is heavily dependent on light availability

When conditions are optimal for photosynthesis, its rate is far greater compared to cell respiration

What are the 6 tissues in a transverse section of a dicotyledonous leaf?

Waxy cuticle

Epidermis

Palisade mesophyll

Spongy mesophyll

Vein

Stoma, guard cells

What is a waxy cuticle?

A wax lipid layer that covers the surface of leaves and prevents uncontrolled and excessive leaf water loss by evaporation

What is an upper epidermis?

Small cells on the upper surface of leaves that secrete a waxy cuticle

What is palisade mesophyll?

A densely packed region of cylindrical cells in the upper portion of the leaf

Contain numerous chloroplasts and are located to receive maximum sunlight for photosynthesis

What is spongy mesophyll?

Loosely packed cells located below the palisade layer and just above the stomata

They have few chloroplasts and many air spaces containing water

Providing a large surface area for gas exchange

What are veins? Where are they located within a leaf?

These structures enclose the fluid transport tubes called xylem and phloem

Veins are located centrally within a leaf, to provide access to all the cell layers

What is the lower epidermis?

Small cells on the lower surface of leaves that secrete a waxy cuticle

Guard cells forming stomata are embedded in this layer

What are stomata (singular stoma)?

Numerous microscopic openings on the lower surface of leaves

Each stoma is composed of two guard cells

What is the function of a pair of guard cells?

A pair of guard cells can create an opening or close it, as needed

When open, stomata permit carbon dioxide to enter the leaf and at the same time, water vapour and oxygen to exit the leaf

At night, plants may close their stomata

Why are stomata located on the lower surface of leaves?

Limits water loss as a result of transpiration, because the lower surface of leaves experiences lower temperatures compared to the upper surface

This is not true for aquatic plants (located on upper surface)

How does the density of stomata fare between species of plants?

Density of stomata varies between species of plants and even varies within a single species based on long-term environmental factors

How can stomata density be expressed?

Can be expressed as number of stomata mm^-2 or micrometers^-2

Is there selectivity for gas transport through stomata?

No

What are four environmental factors that influence the rate of transpiration?

Increased light

Increased temperature

Increased wind speed
Increase humidity

How does increased light affect the rate of transpiration?

Increases rate of transpiration

Light stimulates guard cells to open stomata

If a lack of light results in stomata being closed, the rate of transpiration will be zero (thus, changing the other factors will have no effect)

How does increased temperature affect the rate of transpiration?

Increases the rate of transpiration

Increased molecular movement, including increased evaporation of water

How does increased wind speed affect the rate of transpiration?

Increases the rate of transpiration

Wind removes water vapour at the entrance of stomata, thereby increasing the water concentration gradient between the inside and outside of the leaf

How does increased humidity affect the rate of transpiration?

Decreases the rate of transpiration

Increased humidity lessens the water concentration gradient between the inside and outside of the leaf

What are the 2 main differences between xylem and phloem?

Water in the xylem only moves up (in one direction)

Sugar solution moves in both directions within phloem

Xylem tubes are dead, phloem tissue is alive

What is the difference in the location of phloem and xylem, as well as meristematic tissue?

Phloem are always located farther out compared to xylem

Meristematic tissue is located between phloem and xylem — called vascular cambium

Differentiates into phloem and xylem as the stem gets larger

What is sap?

Fluid rich in sugars that is transported through the phloem

What is a source?

A plant organ that is a net producer of sugar, either by photosynthesis or by hydrolysis of stored starch

Ex. leaves

What is a sink?

A plant organ that uses or stores sugar

Roots, buds, stems, seeds, and fruits are all sugar sinks

What is an example of a structure being used both as a source and sink?

A root structure can store sugar or break down starch to provide sugar, depending on the season: root storage structures such as potatoes act as sinks in the summer and as sources in the early spring

What is the cellular structure of phloem?

Two cells that pair together into a functional unit and create a tube-like vascular network throughout the plant

Two cells: Sieve tubes and companion cells (both living)

How are sieve tube elements formed?

Individual phloem sieve tube cells are connected to one another by porous sieve plates

Sap travels through the tube-like area of the sieve tube elements where the plasma membrane and cytoplasm are greatly reduced

What is the role of companion cells?

Metabolic activities of companion cells allow sieve tube elements to remain alive

Sieve tube elements do not contain a nucleus and many other important cell organelles, because they are designed to be nearly empty to serve their function as vessels carrying a fluid

How are companion cells and sieve tube elements connected?

Have multiple connections called plasmodesmata

These allow the cytoplasm of the tube cells to be shared and are the origin of the proteins and ATP needed by the highly specialized sieve tube elements

What is translocation?

The movement of sap within the sieve tube elements and occurs because a water pressure is created at the source

Companion cells in the source actively transport sugar molecules in, and the sugars pass through the plasmodesmata into the sieve tube elements in that area

Describe the process of translocation.

Movement of sugars into an area of sieve tube elements creates an area of low water potential because of the high number of solutes

A nearby xylem vessel will release water into the sieve tube element, as the water will move from an area of high water potential (xylem) to low water potential (phloem) by osmosis

Influx of water increases pressure

The water, now rich in sugars, moves through the sieve plates within the tube created by the sieve tube elements

Area of low pressure is wherever sugars are being downloaded out of the sieve tube elements, into companion cells and then to an area where the sugar is needed for energy or storage

In the area of the sink, because solutes are being removed, water returns to a xylem vessel by osmosis

What are sessile organisms?

Cannot move from place to place, but are still able to alter their body form in response to environmental stimuli

Example: venus flytrap

What is a venus flytrap?

A carnivorous plant native to wetlands

Plant species lives in soils that are deficient in minerals especially nitrogen - Thus, it requires adaptations

What is the venus flytrap’s “trap”?

“Trap” is a pair of leaves with short but sturdy trigger hairs

Fly trap waits for an insect to crawl or fly inside its paired leaves and trigger the hairs

Within a second of the hairs being triggered, the leaves close around the prey animal, to prevent it from escaping

Internal portion of these leaves then secretes enzymes to digest the trapped insect

What are meristems and meristematic cells?

Meristems are areas of special tissue found in plant cells

Meristematic cells are undifferentiated cells that can divide rapidly, allowing growth in plants

What are the 2 major types of meristematic tissue?

Apical and lateral tissue

Where and what is apical meristematic tissue?

Occurs in root tips and at the tips of branches

Apical tissue enables a plant to lengthen through mitosis

Where and what is lateral meristematic tissue?

Occurs in stem tissue and enables the stems to grow in width

What is the “zone of cell division”

The area where new, undifferentiated cells are formed

What are the two types of roots?

Taproots (ex. carrots) - thick, central root that grow vertically into the soil

Root hairs

What are root hairs?

Responsible for water absorption as they increase surface area

Cooperate with fungi

Fungi have a symbiotic relationship (fungi increases surface area for water absorption, fungi takes sugar)

Fungi/root association called mycorrhizae

What is the adaptation of the roots of grass?

Grass have fibrous roots: shallow and more efficient in water absorption when the rain immediately comes

What do the rings of bark tell us about the age of a tree?

1 ring = 1 year

Thickness tells us about the climate/weather that year

How do plants grow relative to the location of their seed?

As sessile organisms, plants live out their lives where a seed takes root

As the seedling shoot begins growth, it is often in an area where the greatest light availability is in one direction only

What is phototropism?

A mechanism that enables directional growth towards greatest light availability

What is tropism?

Any directional growth response to an external stimulus

Why is phototropism categorized as positive tropic resonse?

Because the plant growth is towards the light stimulus

What is positive tropism vs negative tropism?

Positive - in the direction of the stimuli

Negative - opposite of the direction of the stimuli

What are hormones produced by plants called?

Phytohormones

What is the function of auxin?

Results in plant cell elongation

What is the function of cytokinin?

Increases rate of cell division

What is the function of ethylene?

Promotes fruit ripening

What is the function of gibberellin? When is it formed in the germination of a seed?

Controls stem elongation, seed germination, flowering, and dormancy

Formed after water absorption

Where is auxin produced?

In the growing region of plants, specifically in the tips of shoots and roots and growth buds

Under certain environmental influences, auxin is evenly concentrated in an area of growth and cell elongation is uniform in that area

How is auxin transported throughout the plant?

Auxin can enter phloem tissue and be moved throughout the plant within phloem sap

How can auxin enter and exit a cell?

Requires membrane proteins known as auxin efflux carriers to exit a cell

This is a type of active transport because ATP is required

Why would a plant tissue change the position of the auxin efflux carriers?

To change auxin concentration when light availability changes

A plant distributes efflux carriers predominantly on one side of a series of adjoining cells to encourage a one-way movement of auxin through that series of cells

What is an auxin source?

Any area of growing tissue in a plant, such as the tip of a plant shoot

What is an auxin sink?

The area of plant tissue that auxin is moving towards

Auxin efflux carriers are distributed within each cell so that they are close to the auxin sink

Auxin cannot move backwards towards the auxin source, because the carrier proteins are not located on that side of the cell

What does cell elongation in plants necessitate from cell walls?

Necessitates an increase in length of plant cell walls

Can only occur if cross-linking fibres of cellulose are first loosened

How are cross-linking fibres of cellulose loosened?

Auxin promotes loosening

What happens when auxin first enters a cell?

When auxin enters a cell, it promotes the synthesis of proton pumps

Auxin also binds to the proteins making up the hydrogen pumps and stimulates their insertion into the plasma membrane of the cell

What do the hydrogen pumps do?

Using ATP as an energy source, the pumps move hydrogen ions from the interior of the cell through the plasma membrane

Concentrates the protons in an area called the apoplast

What is the apoplast? What do the hydrogen ions do here?

Any area of adjoining plant cells outside the plasma membranes

Includes the cell wall and any intracellular spaces between cell walls

The hydrogen ions activate a protein called expansin already found within the cell wall

What does expansin do?

Expansin loosens the hydrogen bonds that cross-link cellulose fibres, allowing the fibres to move past each other into new positions

Absorption of the water will create high internal turgor pressure, creating the force necessary for the fibres to slide past each other

Fibres of cellulose make new hydrogen bonds in their new positions

Result: longer cell walls and elongated cells

What is the position of auxin efflux pumps in relation to sunlight (for phototropism)?

Plants position auxin efflux pumps on the shaded side

The presence of auxin results in elongated cells on the shaded side and results in a curved growth pattern towards the light

Where is auxin and cytokinin produced and what does this mean?

Auxin is produced in the shoot growing region, whereas cytokinin is produced in the root growing region

This means that both hormones must be transported to affect a region of growth where they are not produced

What favours development of roots vs development of shoots?

High auxin to cytokinin ratio favours development of roots

High cytokinin to auxin ratio favours shoot and bud development

How is cytokinin transported?

Cytokinin is transported in xylem fluid, because the direction of that fluid is from the root towards the shoot

When does the best plant growth occur?

At certain concentrations, two hormones work

What phytohormone plays a role during ripening?

Fruits produce a gas called ethylene (aka ethene)

Because ethylene is a gas, when one fruit begins to ripen and produce ethylene, any adjacent fruit is exposed to the gas, and all the fruit then ripen quickly and at the same time

This is an example of a positive feedback mechanism