BISC 101 Test 3

Physiological Response Drought Example

Physiological Response Drought Example

• Shorter term

• Close stomata

• Shed leaves

• Alter water transport

Phenotypic Plasticity Drought Example

• Longer term

• Grow smaller leaves

• Increase root growth

• Make a thicker cuticle

What does vascular plants include?

• Flowering plants

• Conifers

• Ferns

Shoots Function

• photosynthesis

• water transport

• defense

• gas exchange

• reproduction

• Structure stability

Roots Function

• Anchoring the plants

• Absorbs water and nutrients

• Storage of food

• Stability roles

• transport systems

Reproductive Shoot (flower)

• Originate from the axillary buds of the stem. Their role is sexual reproduction and the formation of new member of species

Apical Bud

• Responsible for the primary growth and the elongation of the main stem. Located at the top of a flower

Node

• Responsible for the growth of new structure like leaves, flowers, etc. Located on the stem

Internode

Provide the distance between the node and internode and are important of the growth of leaves, flowers, branches, etc.

Vegetative Shoot (Branch)

• Protects the developing buds and attract the pollinators as well as being responsible for photosynthesis, sexual reproduction, transpiration, etc. Comes up out of the ground, consisting of the stem and the trunk.

Leaf: Blade

a large, broad, flat surface that has many layers that not only help the plant move but also help it store materials and byproducts of photosynthesis.

Leaf: Petiole

Helps to twist the leaf to face the sun. It allows the transport of the energy synthesized in the leaf to the rest of the plant. It also enables the transport of nutrients and water to the leaf.

Stem

Transports water and nutrients up from the roots all the way to the leaves, and the stem transports sugars from the leaves to the rest of the plant

Taproot

To provide deep anchorage. It also aids in the absorption of nutrients and water from the soil.

Lateral branch roots

Increase the volume of soil reached by the root, provide anchorage, and participate in water and nutrient uptake and transport. It branches off from other roots.

The Three Types of Tissues in Plants

• Dermal

• Vascular

• Ground

Dermal Tissue Function

• Protection, structural components, acts like a cell membrane in terms of absorption and gas exchange

Vascular Tissue Function

• Transportation

Ground Tissue Function

• Nutrient storage, photosynthesis, physical support and metabolism

Key Components in Plant Cells

• Cell wall - rigid

• Chloroplasts - photosynthesis

• Vacuoles - storage

Dermal: Epidermal Cells

Protection

• in shoots: secrete waxy cuticle

• prevents infection and water loss

Absorption

• in roots: extend root hairs

• increase SA:V ratio

Dermal: Guard Cells

Gas exchange

• Border stomata

• Open and close to regulate gas exchange

Dermal: Trichomes

Protection

• Physical irritant

• Production of sticky or noxious chemicals

Can be made of single or multiple cells

Vascular: Xylem

• Transport water and minerals

• Physical support

• Long-distance signalling

Vascular: Phloem

• Sugar transport

• Long-distance signalling

Ground: Parenchyma

• Photosynthesis (in leaves) or starch storage (in roots)

• Thin cell wall

Ground: Collenchyma

• Flexible expandable structure (ex. celery)

• Thick cell wall

Ground: Sclernchyma

• Rigid, permanent structure

• Usually not alive

• Very thick cell wall

• Examples: fibers, nut shells

How do plants grow?

Cells in apical meristems divide and differentiate

• Apical meristems occur at:

  • Buds (shoots)

  • Root tips (roots)

Cells in apical membranes divide

• Stem cells in meristems are able to continuously divide

• Produce other cell types and self-renew with each cell division

Cells in apical membranes differentiate

• Cells differentiate when they acquire a specific structure and function

  • muscle cells in humans

  • parenchyma in plants

Primary growth

Allows root and shoot tips to extend body outwards. The root cap protects the delicate dividing cells. Once a stem or root is made, it does not move.

Secondary growth

Cells in vascular cambium (lateral meristems) divide and differentiate. This causes stems to grow wider

• Cells on one side become xylem, on other side become phloem. example of secondary growth

Secondary growth Wood Example

• The secondary xylem produced by the vascular cambium

Secondary growth Bark Example

• Tissues outside of the vascular cambium

A stem cross section

• The original primary growth remains in the stem centre

• The vascular cambium continues to produce secondary xylem and phloem over time

• Once secondary xylem is produced, it does not move within the stem

What are plant cells made of?

• Lipids (C, H, O)

• Carbohydrates (C, H, O)

• Proteins (C, H, O, N, S)

• Nucleic Acids (C, H, O, N, P)

Essential nutrient

A nutrient needed for survival, that must be taken in from the environment. Missing essential micronutrients can have a significant effect on plant health

What do essential nutrient do?

• Enzyme cofactors

• Chlorophyll components

• Water/Salt/Electrical balance

How do plants get nutrients

Most nutrients (other than CO2) absorbed through roots as ions

Adaptations:

• High SA:V Ratio

• Selective transport across the plasma membrane

• Nutrients can generally pass freely through the cell wall

Membrane transport of ions

First, proton pumps establish an electrochemical gradient

• Proton pump = primary active transport of H+ using energy from ATP

• Creates chemical gradient of H+ and creates charge gradient

Cation diffuse into the cell following their electrochemical gradient

• Concentration and charge both play a role

Anions are actively transported into the cell using proton co-transporter

• Secondary transport against concentration gradient and charge gradients

How to keep substances out of plants?

• Plants accumulate some molecules and exclude others

• Plants require each nutrient within a certain range of concentrations

• Some substances aren’t nutrients at all and are toxic at all levels

Strategy #1: Passive Barrier

• A membrane without specific transport proteins in an effective barrier against ions

Strategy #2: Metallothionenes

• Proteins that bind specific ions and prevent them from acting as a poison

• Ex: Copper is an essential nutrient but toxic at high levels. Plants near copper mines upregulate metallothionen expression to prevent poison(phenotype plasticity)

Strategy #3: Active Transport

• Ion can be transported out of the cell/ plant into the vacuole where they can’t do harm

• Ex: H/Na antiporter uses proton gradient to pump Na against its concentration gradient into the vacuole

Symbiosis

• Some nutrients (N, P) are typically too low in soil to support plant growth(limiting)

• Many plants rely on fungal and bacterial symbionts for help

Fungal symbiosis

Mycorrhizal fungi are symbiotic with 80% of vascular plants

Benefits to the plant:

• Up too 700x greater SA of root system

• Fungal enzymes break down decaying matter, liberating nutrients

Benefits to the fungus:

• Sugar from photosynthesis

Bacterial symbiosis

Rhizobium bacteria are symbiotic with some plants, notably legumes

Benefits to the plant:

• Rhizobia can convert nitrogen gas to organic nitrogen compounds (NH3, NO2) that can be used by plants - nitrogen fixation

Benefits to the fungus:

• Protection from the environment

• Sugars from photosynthesis

Fertilizers

• Natural and synthetic fertilizers are used to increase soil nutrients

Where does water enter in the plant

Water enters root cells by osmosis. (Soil → Roots)

Adaptations:

• Root hairs create high SA: V ratio

• Water travels through roots to xylem

3 Different pathways of travel from roots to xylem

• Apoplastic pathway

• Transmembrane pathway

• Symplast pathway

Apoplastic Pathway

• Water moves through cell walls without crossing any membranes

Transmembrane pathway

• Water enters and exits adjacent cells via the plasma membrane (cell to cell through osmosis)

Symplast pathway

• Water moves between cells via plasmodesmata

Plasmodesmata

• Opening(pores) in the cell wall and plasma membrane of neighbouring plant cells

• Creates a channel of continuous cytoplasm

Endodermis

Layer of cells around the vascular tissue

Water must cross the Casparian strip

• Cells secrete waterproof Casparian strip - blocks apoplastic pathway

• All water must cross at least one plasma membrane to access the xylem - allowing plants to regulate transport of ions and toxins

Why are there multiple pathways for water through the root?

• Multiple pathways increase the speed of water flow through the root

Why allow apoplastic flow if it’s just going to be blocked by the Casparian strip

It’s VERY FAST

Xylem cell types

• Tracheids and vessel elements (only in some vascular plants)

Adaptations:

• Pits and perforations allow unimpeded water flow (holes)

• Thick cell walls allow high water pressure

• Cells are dead and “empty” at maturity, increasing water volume

• Water moves through the xylem by Bulk Flow thanks to low resistance of xylem cells

Water lost from leaves by transpiration

• Water evaporates and exits leaves through stomata

Water potential

Potential energy of water

• Water moves towards lower(more negative) water potential

Factors affecting water potential:

• Solute concentration - solute potential

• Pressure (ex. bulk flow) - pressure potential

Water potential drives water transport

Air: changes with humidity; usually very low

Leaf: depends on transpiration rate; lower when stomata open

Soil: depends on soil moisture; high if soil moist

The Cohesion-Tension Theory

• Water forms a continuous chain through the xylem due to hydrogen bonds (cohesion)

• Tension caused by water evaporating (transpiration) pulls water upward

An analogy:

• Sucking water through a straw ~0.1 MPa

• Car tire pressure ~0.25 MPa

• Tension in xylem up to 2MPa

Transpiration drives water flow

• Stomata are a key point of regulation. Critical movement of water

Guard cells open when vacuoles are swollen

Water filling the vacuole of guard cells changes the shape of the cell, opening stomata

Why do plants need water?

Plants need water for structure, photosynthesis and cellular respiration

Phloem cell types

Sieve elements and Companion cells

Sieve elements

• The cells that do the long-distance transport

• Connected to each other by sieve plants - many plasmodesmata

• Lack many organelles to allow free sap flow (ex. nucleus, Golgi)

Companion cells

• The cells that provide metabolic support to the sieve elements

• Connected to sieve elements by plasmodesmata

Phloem transport sugar throughout the plant

Key steps:

• Phloem Loading

• Bulk Flow

• Phloem Unloading

Phloem loading at the source

1. Sucrose moves from site of photosynthesis or storage into companion cells then into sieve tube elements

2. Transport to the companion cells can be passive or active depending on relative concentrations. Active transport relies on proton/ sucrose symporters

3. Transport to the sieve tube elements occurs by diffusion through plasmodesmata

Phloem sap is transported by bulk flow

1. Sucrose loading increases solute concentration in phloem

2. Water enters phloem from xylem by osmosis

3. Turgor pressure pushes sap through phloem by bulk flow

This is the pressure-flow mechanisms of sugar transport

Phloem unloading at the sink

• Sucrose moves from sieve tube elements, to companion cells, and to parenchymal sink by passive transport (down concentration gradient)

• Water is absorbed back into the xylem by osmosis as solute concentration decreases

The concentration gradient between companion cell and parenchyma cells is maintained by two different approaches:

• By actively packing sucrose into vacuoles

• By actively using up the sucrose

Xylem Transport

Roots → Leaves

Phloem Transport

Leaves → Everywhere

Order for xylem

1. Soil → Roots

2. Roots → Xylem

3. Xylem

4. Xylem → air

Epiphytes (air plants)

• Do not absorb nutrients from soil

What adaptations could help epiphytes acquire nutrients?

• Have specialized structure to absorb nutrients

• Leaves pool & absorb water

• Shoot systems absorbs nutrients (catch dust in trichomes)

Carnivorous plants

• Absorbs nutrients from prey

What adaptations help carnivorous plants acquire nutrients?

• Modified leaves/ root trap insects

• Enzymes secreted to digest prey

• Nutrients absorbed through shoot or root systems

How do animals sense the environment?

Specialized organs/ tissues

• Ears

• Movements

• Sight

• Touch

• Taste buds

• Odour receptors

• Pain receptors

• Temperature receptors

Interpreted by nervous system

How do plants sense the environment?

• Sensing molecules/ cells distributed throughout the plant

• Signals sent to other tissues by hormones

• light, gravity, temperature, water, stiffness of soil, wind, damage, communication from other plants

Sensory cell

• Perceives external stimulus

• Releases hormone (cell-cell signal)

Target cell

• Perceives cell-cell signal

• Responds

Which vascular cells would expect hormones to travel through?

• Phloem (leaves → everywhere)

How are target cells specifically selected?

The right receptor is required for the hormone (signalling molecule) to take effect

Signal Transduction pathway

• Signal (hormone) binds receptor

• Cascade of intracellular events

• Cellular response

How do target cells respond to hormones?

1. Signalling hormone binds receptor

2. Signal transduction transmit the signal from the receptor to the response machinery

3. Cells responds to signal

What responses occur in response to hormones

An increase or decrease in:

• Expression of specific genes (transcription)

• Activity of specific enzymes

• Activity of membrane transport proteins

A direct response to light stimulus - the mechanism

1. Photoreceptor detects light, and a signal is transduced

2. Increased pumping of H+ ion out of the cell via H+ pump (using ATP)

3. Ions (e.g. K+) and sugars can now move in

4. Following its potential, water flows in

5. Cells swell - stomata open, allowing gas exchange

In response to low water in the roots:

1. Roots make ABA, send it to the leaves via xylem

2. ABA is sensed by guard cells and a signal is transduced

3. H+ pump is activated

4. Ion channels open up; K+ can move out

5. Following its potential, water flows out

6. Cells are no longer full of water; pore closes

In response to low humidity in air:

1. Leaves make ABA, send it to the roots via phloem

2. ABA is sensed by root meristem cells and a signal is transduced

3. Changes in gene expression accelerate cell division

4. Roots grow faster to access more water

Basic Framework of Cell Response

Signal/ hormone → Signal is transduced → Cellular response

Plant Defence Classes

• Physical

• Chemical

Constitutive Defences

• Are always present, regardless of whether an herbivore, pest or pathogen is present

Plant Defences

• Herbivores

• Pathogens: Viruses, Fungi, Bacteria

Induced Defences

• Are triggered when a plant is attacked. Can start to mount defences to prepare for possible attacks

Plant Physical Defences: Waxy Cuticle

• Is difficult to penetrate and slippery

Plant Physical Defences: Trichomes

• Can injure or slow down herbivores or make surfaces sticky