Biology 3A - homeostasis

The organism and its environmentOrganisms have needs and produce wastes

They must survive in environments that may be inconstant and harsh, and thus must have features that allow their survival

Some of the most important environmental challenges include dealing with temperature extremes, water salinity and water availability

In this section we look at how different organisms meet these challenges in order to survive

Cells need matterNutrients and essential materials include:• Organic compounds (contain Carbon) eg glucose,

proteins, fats, DNA, RNA, ATP

used for body structures, cell components, enzymes, hormones, etc

• Inorganic elements or compounds eg nitrogen, phosphorus, calcium, iron, sodium, potassium, etc

used for making organic compounds (eg proteins, DNA & ATP contain nitrogen and phosphorus), maintaining osmotic balance, and pH balance

Cells need to remove wastesDescribe the effects of these on the cell:

• Carbon dioxide toxic waste, decreases pH

• Ammonia toxic waste, increases pH

• Excess salts alters osmotic pressure – drags in water

• Excess water alters osmotic pressure – can burst cells

Exchange of material

Occurs at the cell membrane

The processes involved include osmosis, diffusion and active transport

Exchange of material 2Permeable substances can move through

Differentially permeable only some substances can move through

Hypotonic lower salt concentration

Hypertonic higher salt concentration

Isotonic same salt concentration

Concentration gradient difference in concentrations across membranes

Osmotic pressure force that pulls water across a membrane, due to concentration gradients

Size and surface area

As size increases what happens to surface area to volume ratio? SA:Vol decreases

Why is this important? Exchange occurs at surfaces – the larger the SA:Vol, the more exchange will occur

Shape and surface areaWhat happens if cells change shape? – alters surface area

2x 2x2

1x1x8

4x2x1

How cells increase their surface area

• Size • Shape• Folding • Cell extensions

pseudopods

microvilli

Cells need energy

Energy in the cell is transported as ATP

Cells can get energy by:

Respiration (all cells)

Photosynthesis (plants)

Respiration• Glycolysis glucose pyruvate + 2 ATP

• Fermentation (plants) pyruvate alcohol + CO2

• Fermentation (animals) pyruvate lactic acid• These all occur in the cytoplasm• Transition reaction pyruvate enters mitochondrion

and the Krebs cycle • Krebs cycle – series of reactions that generates

ATP, H2O & CO2 and uses electron transport chain to generate large amounts of ATP (34 – 36 ATP)

Summary of respiration

Comparison of aerobic and anaerobic respiration

Anaerobic Aerobic

Site it occurs Cytoplasm Mitochondria

Need for oxygen No Yes

Waste products Lactic acid (animals)

Alcohol + CO2

(plants)

CO2 + H2O

Amount of ATP 2 34 - 36

Reactions involved

Glycolysis, fermentation

Transition, Krebs, electron transport

chain

Photosynthesis

• Light dependent reactions

Occurs in grana

Photosystems I and II use light to split H2O into H+ and O2

Electron transport chain generates ATP• Light independent reactions

Occurs in stroma

ATP & H+ from light reactions used with CO2 in Calvin cycle to make sugars glucose

Summary of photosynthesis

Comparison between respiration and photosynthesis

Respiration Photosynthesis

Inputs Oxygen and glucose Light, CO2 and water

Products ATP, CO2 and water Oxygen and glucose

Type of cells All Plants, some protists & cyanobacteria

Location in cells Cytoplasm and mitochondria

Chloroplasts

Where energy comes from

Organic compounds eg glucose

Light

Role of ATP End product Made in light reactions, used up in dark reactions

Names of reactions Glycolysis, fermentation, Krebs cycle

Light reactions, Calvin cycle

Factors affecting rate of respiration

• Temperature as temperature increases, respiration increases, until temperature gets too high enzymes denature

• Concentration of glucose as glucose increases, respiration increases, until maximum level reached

• Concentration of oxygen as oxygen increases, respiration increases, until maximum level reached

• Concentration of wastes (CO2 or alcohol) as wastes increase, respiration decreases

Factors affecting rate of photosynthesis

• Temperature as temperature increases, photosynthesis increases, until temperature gets too high enzymes denature

• Light as light increases, respiration increases, until maximum level reached

• Concentration of carbon dioxide as carbon dioxide increases, respiration increases, until maximum level reached

• Humidity if humidity decreases, stomata will close to conserve water, hence reducing carbon dioxide, and slowing photosynthesis

Enzyme terminologyActive site where substrate attachesSubstrate what enters a reactionProduct what leaves the reactionEnzyme-substrate complex substrate attached to

enzymeLock and key model enzyme & substrate match

like a key into a lock

Factors affecting enzyme functions• Temperature as temperature increases, reaction rate

increases, until temperature gets too high enzymes denature

• pH enzymes are pH specific – only work in specific pH range

• Concentration of substrate as substrate increases, reaction rates increase, until maximum level reached

• Concentration of product as products increase, reaction rates decrease

• Concentration of enzyme as enzyme increases, reaction rates increase, until maximum level reached

• Cofactors as increase, rate increases• Inhibitors as increase, rate decreases

HomeostasisMaintenance of constant internal environmentThis involves continually replacing substances as they are used up (eg glucose, oxygen) or continually removing substances as they build up (eg wastes)

Negative feedback systems

• Stimulus change in conditions• Receptor detects the change• Modulator decides what to do about the

change• Effector part of the body that carries out

the response• Response change in activity• Negative feedback response alters the

stimulus in the opposite direction

An example of negative feedback

Stimulus

Negative feedback Receptor

Response Modulator

Effector

Exercise causes increasedcarbon dioxide & decreased oxygen

brain

brain

heart

Heart rate increases

Increased oxygen supplied to muscles