Homeostasis: staying within limits

News paper Article…….

What happened?What part of the body does it affect?

Body cells require a relatively stable internal

environment for normal functioningThe external environment is composed of the environment.The internal environment is the liquid. This includes tissue fluid and plasma.

Extra- and intracellular fluids

Tissue fluid and plasma move. 3 examples include:•Nutrients & gas that pass from tissue fluid to blood•Waste products from tissue to blood•Oxygen from tissue to cells

Homeostasis: keeping within

limitsDespite changes in the external environment, the internal environment of living things remains fairly constant.

The maintenance of a constant internal environment is known as homeostasis.

Systems involved in homeostasisThe systems involved include:

1. Circulatory system2. Respiratory system3. Urinary system4. Nervous system5. Hormonal6. Digestive7. Skin

Variables associated with

homeostasisNutrientsIons (Na+, Ca+, Cl-)WaterBlood volumeRed blood cellsTemperatureOxygen levels

TaskExplain why each of the above variables is

important in maintaining stability.

Detecting and Responding

In order to maintain stable conditions, organisms need to:

•Detect changes•Counteracting change

This type of control is known as negative feedback.

Negative Feedback

What variables are controlled by

negative feedback?Blood glucose levelsTemperatureWater balanceOxygen concentrationpH levelsetc

Hormones in actionControlling blood glucose

levelsThe hormones involved in controlling this variable are insulin and glucagon.

These hormones are produced in the pancreas.

Blood glucose levelsInsulin – controls how much glucose is absorbed, from the blood, by the cells

Glucagon – notifies the liver to release glucose into the blood

Blood glucose levelsAlpha cells – increase production of glucagon which acts on the liver to convert glycogen to glucose

Beta cells – decrease production on insulin. Therefore less glucose will be absorbed by the cells

If the blood glucose levels

fall…

Cells involved....Beta cells

Reduces insulin in the blood

Less glucose being absorbed

Blood glucose levels rise

Cells involved....Alpha cells

increases glucagon production which acts on the liver

Liver converts glucagen into glucose

Blood glucose levels rise

If the blood glucose levels

rise…

Cells involved....Beta cells

Increase insulin in the blood

More glucose being absorbed

Blood glucose levels falls

Cells involved....Alpha cells

Decrease glucagon production which acts on the liver

Blood glucose moves into liver and converted to glucogen

Blood glucose levels falls

Example

Positive Feedback

The change is encouraged

Example is child birth

Cell Communication

Multicellular organisms are composed of many cells.

Communication can either beChemical Electrical

They are referred to as signalling molecules

Hormones as cell communicators

This is an example of cell communication

Hormones can travel different distancesAction on the same cellDiffusion through tissue fluid (action on nearby cells)

Transport through the blood stream (action on distant cells

Hormones are diffused through the body

Cells have receptors which are specific to each hormone.

Cells can either have one or many different kinds of receptors for different hormones

Different types of hormones

There are three types of hormones

Amino derivativesSteroid hormonesPeptide hormones

Amino Acid derivativesWhen are they made…

Made in advance by cells and then stored

Life spanShort life span

SolubilityWater soluble

ExampleAlanine

Steroid hormonesWhen are they made…

Made on demandLife span

Long life spanSolubility

Lipid solubleExample

Estrogen

Peptide hormonesWhen are they made…

Made in advance by cells and then stored

Life spanShort life span

SolubilityWater soluble

ExampleAntidiuretic hormone

Steroids have a lipid base, therefore are referred to as hydrophobic (lipophilic) and is insoluble in water

A carrier protein is needed for this hormone to travel through the blood stream.

Amino acid derivatives & peptide hormones are hydrophilic and is soluble in water.

No assistance to travel through the bloodstream

Unable to pass through the membrane without assistance

A G-protein is needed to transmit their message

The difference is how they enter their target cell.

General Pathwaya) Hormone binds to receptor

on cell membrane or within cellb) Signal detected within cellc) Signal transduction a series

of events that changes the signal received by the cell

d) Cell activates response to signal

Hormones in plantsPlant growth and development is influenced by both internal and external factors

Internal factors include: chemicals

External factors include: light, gravity, temperature & day length

TropismsPlants that respond to external factors are known as tropisms.

Some includePhototropismGeotropismThigmatropismPhotoperiodism

PhototropismExternal Factor

LightHormone involved

AuxinResponse

Plant moves towards the light

GeotropismExternal Factor

gravityHormone involved

AuxinResponse

Roots grow towards the earthShoots grow towards the sky

ThigmotropismExternal Factor

touchHormone involved

AuxinResponse

Plant grows along like a vine

PhotoperiodismExternal Factor

Amount of day lightHormone involved

florigenResponse

Flowers open and close to increase pollination

Plant hormonesPlant hormones are

produced by plant cells and in relatively small amounts.

They travel via the phloem and xylem and act on other cells in the plants

Plant hormone classification

Plant hormones are grouped into the following five groups

1.Auxin2.Cytokinins3.Gibberellins4.Ethylene5.Abscicic acid

AuxinProduced in…

The tip of the coleoptileEvidence…

Tips were removed and grow no longer occurred

When tip was placed onto agar, which was then placed onto coleoptile without a tip it grew

AuxinFunction at low concentration

Enlarges and elongates cellsStimulates elongation of young developing shoots and roots

Involved in fruit development.

AuxinFunction at high concentration

Inhibits growth in roots

IAA…Indoleacetic acidInfluences growth and

development in plants (enlargement and elongation of plant cells)

Apical DominanceLateral buds do not

grow and the concentration of growth is located at the apex (top/tip) of the plant

If tip removed lateral buds will grow

Tip removed from a growing shoot

If the tip is removed growth will no longer occur

This is because auxin is stored in the tip. When removed no cell development occurs

If tip is removed and placed onto a piece of agar that auxin store in the tip will diffuse into the agar

When agar is placed onto the growing shoot (tip removed) the shoot will continue to grow

What does this experiment illustrate?

PhototropismPlants move

towards the sunlight. Why?

To obtain more light, so that photosynthesis is maximised

Stimulus: Light

How does it work?Coleoptile A

Light is evenly dispersed Therefore auxin is evenly

dispersed Coleoptile grows straight

Coleoptile B Light is concentrated on one side Auxin moves away from light

source (ie dark side) Highly concentrated on the darker

side causes cells to elongate and grow faster than the other side. This causes the shoot to bend towards the light

Positive phototropism moves towards the light

Negative phototropism

moves away from the light

Worksheet…Investigating phototropism page 19

Hormonal plants – plant growth regulators page 28 - 29

GeotropismRoots and shoots

will change direction if a pot is turned on its side. Why?

So that roots will direct itself to water and shoots towards light

Stimulus: Gravity

How does it work?Roots

Gravity is concentrated on the lower side Auxin is concentrated on the lower side which

cause inhibition of cell growthUpper side grows fast causing it to turn

ShootsAuxin accumulation in the shoots on the

lower sideIncreases cell growth and elongationShoot bends upwards

Positive geotropism moves towards the gravity

Negative geotropism moves away from the gravity

Worksheet…Investigating geotropism page 21

CytokininsProduced in

The roots and can be translocated to the shoots

Its function is to…Growth promoting hormone which acts on shoots, roots and fruits

promote cell division and differentiation

GibberellinsProduced in

The seedIts function is to…

Stimulate stem elongation by stimulating cell division and elongation.

Stimulates bolting/flowering in response to long days. Breaks seed dormancy and initiate bud development

Stimulates enzyme production (a-amylase) in germinating cereal grains for mobilization of seed reserves.

Can delay aging in leaves and citrus fruits.

Abscisic AcidProduced in

The leavesIts function is to…

Stimulates the closure of stomata Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots.

Induces seeds to synthesize storage proteins.

Has some effect on induction and maintenance of dormancy.

EthyleneProduced in

A variety of tissue typeIts function is to…

Stimulates the release of dormancy. Stimulates shoot and root growth and

differentiation (triple response) Stimulates leaf and fruit abscission. Stimulates flower opening. Stimulates flower and aging. Stimulates fruit ripening.

Nervous SystemIs composed of the brain,

spine and nerves around the body

They are categorised into the following groupsCentral nervous systemPeripheral nervous system