Bio II_Final Module

Shoot system

• Usually above ground

• 2 components:

  • vegetative (stems & leaves)

  • reproductive (flowers & fruits)

• Photosynthesis

Root system

• Usually underground

• Physically supports the shoot system

• Absorbs water + minerals

Node

Point of attachment

• mostly for leaves and flowers

Axillary bud

• Located in the axil (area between base of leaf and stem)

• Gives rise to a branch or a flower

Apical bud

Located at the apex (tip) of the shoot

Petiole

The stalk that extends from the stem to the base of the leaf

Trichomes are …

Small hairs on the leaf surface

• can reduce herbivory by hampering insect movement across leaves

• can store herbivory-deterring chemicals

• can reduce rate of water loss by disrupting airflow across leaf surface

Two types of root

• Fibrous root → monocot root

• Tap root → dicot root

Primary growth

• Lengthening of plant

• Growth in length

• Production of leaves

• Production of branches

Secondary growth

• Widening of plant

• Growth in girth in stems and roots

Meristems

The sites of plant growth

• 2 types:

  • Apical meristems → causes primary growth

    • occurs at tips of shoots and roots

    • produces new leaves and flowers

  • Lateral meristems → causes secondary growth

    • occurs at the cambium

    • produces bark on trees

Plant hormones are transported throughout the plant via the _____ ______

Vascular system

Hormones are …

Chemical messengers produced by various parts of the plant

• help regulate growth + development

Phototropism

Plants growth towards light

• plants must respond as environment changes, but can’t move like animals

• Auxin = plant growth hormone that causes plants to grow away from or towards light

Positive phototropism

• Shoots exhibit this

• Towards the light

Negative phototropism

• Roots exhibit this

• Away from light

Tree rings show …

Secondary growth

• rings can be used to track annual growth + thickness provides info about environment conditions in past years

What moves water and nutrients around a plant?

Vascular tissues

• Xylem

• Phloem

Xylem

Carries water & nutrients through “dead” cells from roots to leaves

• moves only in one direction (roots → leaves)

Phloem

Carries nutrients + hormones ( in water)

• moves in both directions

Vascular bundles

Veins in the shoot system

• plant stems vary in their arrangement of these

Water moves from areas of _____ to areas of ______

High water potential'; low water potential

Water potential

The potential for water to do work

• is influenced by pressure & solute concentration

  • adding solutes = decreased water potential

  • adding pressure = increased water potential

Water enters root cells causing …

The membrane to expand into the cell walls & creating turgor pressure

• increases water pressure & turgor pressure

• so watered plants are firm due to turgor pressure

When dehydrated, plants …

Wilt due to lack of turgor pressure

From the roots, water is transported to the ….

Xylem

• increased water pressure (from turgor pressure) in the root cell causes water to leave the root cell and enter the xylem

The Casparian strip helps keep ….

Absorbed water inside the roots

• serves as a boundary layer separating the cortex from the vascular tissue, blocking diffusion of material between them → blockade forces water & solutes to pass through plasma membrane to reach xylem

Properties of water

• Cohesion: water molecules “sticking” to each other

• Adhesion: water molecules “sticking” to other materials

What is capillary action caused by?

Cohesion and adhesion working together

• helps drive water up a plant through the xylem

The width of the vessel elements is under ____ ____

Selective pressure

Narrower vessels can better withstand …

Pressure from drought

Wider vessels can transport ….

A greater amount of water & carbon

Water is lost through …

Transpiration at the leaves

• plants have to open stomata to bring in more CO₂ and get rid of excess O₂

• Transpiration: water vapor is also lost when stomata are open

Water moves up a plant due to …

Combination of forces

• positive water pressure in roots due to water entering

• negative water pressure in leaves due to transpiration

• capillary action through xylem

Sugars move from sources to sinks (translocation) via …

Water potential differences

• source = where the photosynthates are coming from

• sink = where the photosynthates are being delivered to

Unlike xylem, phloem flow direction changes based on …

The plant’s needs

• Where photosynthates are directed to in ..

  • Early on: roots

  • Vegetative growth: shoots and leaves

  • Reproductive development: seeds and fruits

  • Highest leaves: send upward to growing shoot tips

  • Intermediate leaves: send products in both directions

  • Lower leaves: send downward to roots

Sieve tube elements

The cell that primarily make up phloem

• have reduced cytoplasmic contents

• connected via sieve plates w/ pores to allow material to move

Companion cells

Keep sieve tube elements alive

Phloem sap

An aqueous solution that contains up to 30% sugar, minerals, amino acids, and plant growth regulators

Form follows function

If a structure is important for survival, then its physical features closely reflect its function

• result of evolution: over time, individuals w/ structures that are more efficient for a specific function have an advantage over individuals w/ structures that are less efficient for that function

• individuals w/ advantage are more likely to survive, reproduce, and pass on that efficient structure to offspring

  • efficient structure becomes more common in population (adaption)

Skin cells

• Function: cover surface of body and line organs and cavities within the body

• Structure: cells are tightly bound continuous layer

Neurons

• Function: transmit electronic signals very rapidly over long distances

• Structure: long extensions

Red blood cells

• Function: bind and transport oxygen and other substances through narrow passages of circulatory system

• Structure: shaped like a disk with indentation in middle

Homeostasis

The body’s ability to maintain a constant internal environment despite changes to the external environment or changes in activity

Components of homeostatic feedback loops

• Stimulus

• Set point

• Sensor

• Control center

• Effectors

Thermoregulation

The body needs to maintain stable temperature

Stimulus

An external event occurs that shifts the body’s state away from the set point

Sensor

Monitors/detects the current state and sends that info to the control center

Control center

Compares current state to the set point

Effector

When the control center detects shift away from set point, it triggers an appropriate response

Blood glucose homeostasis

• Sensor = glucose-sensitive neurons in brain, send messages to the control center

• Control center = pancreas

• Effector

  • a) When blood glucose is too high, pancreatic beta cells release insulin

    • insulin causes cells throughout body update glucose & liver uptakes glucose and converts it into storage form, glycogen

    • b) When blood glucose is too low, pancreatic alpha cells release glucagon

  • Response = when blood glucose is too high, pancreatic beta cells release insulin

    • when blood glucose is too low, pancreatic alpha cells release glucagon

What does insulin cause

• Cells throughout body update glucose

• Liver uptakes glucose and converts it into storage form, glycogen

What does glucagon cause

Liver breaks down glycogen and releases glucose into bloodstream

Negative Feedback

• Counteracts changes to maintain steady state (equilibrium)

• Typically maintaining status quo

• i.e. Predator/Prey Dynamics

Positive Feedback

• Changes promotes further change toward an extreme

• Typically driving a process to completion

• i.e. Contractions during delivery

Feedbacks

Agents of stability or rapid change

Negative feedback control

A change in a variable triggers a response that counteracts the initial change

• “Negative” means response negates the stimulus that disrupted homeostasis

Positive feedback control

A physiological control mechanism in which a change in a variable triggers a response that reinforces or amplifies the change

Osmoregulation

• Stimuli: dehydration or too much hydration/salt concentration in blood

• Sensor: hypothalamus

• Control center: hypothalamus

• Effector: pituitary

• Response: Kidneys reabsorb more or less water, feeling of thirst

Thermoregulation

The maintenance of internal body temperature within a tolerable range, despite changes in environment or activity

Endothermic

• Warm blooded animals

• Metabolically generate their body heat

Ectothermic

• Cold blooded animals

• Rely on environment to produce their heat

Animals exchange heat with the environment through 4 mechanisms:

1. Radiation

2. Evaporation

3. Convection

4. Conduction

Relationship between surface:volume ration and heat transfer

• Smaller animals (which have higher surface:volume ratio), have more rapid heat transfer

• Large animals (which have lower surface:volume ratio), have less rapid heat transfer

Within a species, larger individuals are found in _____, and smaller individuals are found in _____

Colder climates; warmer climates

Where are appendage length longer in populations vs. shorter?

• Longer in populations of same species living in warm climates near equator

• Shorter in populations living further away from equator in colder environments

Where is thermoregulation more challenging?

In aquatic environments

• water wicks away heat faster than air (it has high specific heat)

Counter-current heat exchange

• Conserves heat

  • reduces heat loss in extremities, maintains core body temp (found in many marine species, also in limbs of mammals)

• Works by pairing arteries and veins in close physical contact to exchange heat

  • warm blood leaving the core (artery) warms the cold blood returning to the core (vein)

What happens when cells get really cold?

• Cells have lots of water inside of them → when ice crystals form inside cells, the crystals puncture the cells, killing the organism

Why could organisms lose their nerves?

If metabolic cost of nerve net is high, losing neurons may have been selectively advantageous

Dendrites Function

Receive signals from environments or other neurons

Cell body (soma) Function

Contains nucleus and organelles needed for cellular function

Axon Function

Propagates signal over physical space

Myelin sheath Function

Insulates the axon to speed up propagation of the signal down the axon

• signal is “recharged” at nodes of Ranvier

Axon terminal Function

When signal reaches it, it triggers chemical messages to be sent to dendrites of the next neuron across the synapse

Synapse

Is between two neurons where neurotransmitters are released for cell communication

How are human neurons highly variable?

• There are at least 40 different “types” of neurons

• They vary in:

  • Morphology

  • Density

  • Size

  • Electrical properties

  • Microtubule scaffolding structures

How do neurons communicate?

Via action potentials

Neuronal axons

Contain transmembrane proteins that help regulate membrane potential

Ion channels

Help transport ions into or out of the cell in response to a stimulus

At resting potential, inside the neuron is …

• Negative compared to outside the neuron

• Negative inside due to:

  • anions are concentrated inside the cell

  • Na/K pump moves out more cations than it brings in

  • Potassium leak channels allow K⁺ to leave the neuron

  • Negatively charged proteins inside the cell

The Na+/K+ pump helps …

• Maintain membrane potential through active transport

  • it continuously pumps 3 sodium (Na+) out of the neuron and 2 potassium (K+) into the neuron

At the resting state, all voltage gated channels are ____

Closed

If the resting potential has a charge difference across the member, it’s ____

Polarized