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AP Biology

AP Biology 2006-2007

Homeostasis

Regulating the Internal

Environment

AP Biology

Diverse Forms, Common Challenges

▪ Anatomy: the study of

the biological form

(STRUCTURE) of an

organism

▪ Physiology: the study

of the biological

FUNCTIONS an

organism performs

▪ Structure dictates

function!

AP Biology

Hierarchical Organization of Body Plans

Cells Tissues Organs Organ Systems

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Four main types of tissues:

1.Epithelial: covers the outside of the

body and lines the organs and cavities

within the body

2.Connective: binds and supports other

tissues (cartilage, tendons, ligaments,

bone, blood, adipose)

3.Muscle: controls body movement

(skeletal, smooth, cardiac)

4.Nervous: senses stimuli and transmits

signals throughout the animal

(neurons, glia)

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Coordination and control within a body

▪ Endocrine System: transmits chemical signals (hormones) to all locations in the body through the bloodstream

Slow acting, long-lasting effects

Info received by: cells with specific receptors for released hormone

▪ Nervous System: neurons transmit info between specific locations

Very fast!

Info received by: neurons, muscle cells, endocrine cells

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AP Biology

AP Biology

Homeostasis

▪ Keeping the balance

animal body needs to coordinate many systems all at once▪ temperature

▪ blood sugar levels

▪ energy production

▪ water balance & intracellular waste disposal

▪ nutrients

▪ ion balance

▪ cell growth

maintaining a “steady state” condition

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Conformers vs. Regulators

▪ Two evolutionary paths for organisms

regulate internal environment▪ maintain relatively constant internal conditions

conform to external environment▪ allow internal conditions to fluctuate along with external changes

conformer

thermoregulation

regulator

conformer

osmoregulation

regulator

AP Biology

Homeostasis

▪ Fluctuations above/below a set point

serve as a stimulus; these are detected by

a sensor and trigger a response

▪ The response returns the variable to the

set point

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Negative Feedback

▪ “More gets you less.”

▪ Return changing

conditions back to set

point

▪ Examples:

Temperature

Blood glucose levels

Blood pH

Plants: response to

water limitations

Positive Feedback

▪ “More gets you more.”

▪ Response moves

variable further away

from set point

▪ Stimulus amplifies a

response

▪ Examples:

Lactation in

mammals

Onset of labor in

childbirth

Plants: ripening of fruit

AP Biology

Temperature Regulation

AP Biology

sensor

Negative Feedback Loop

high

low

hormone or nerve signal

lowersbody condition(return to set point)

hormone or nerve signal

gland or nervous system

raisesbody condition(return to set point)

gland or nervous system

sensor

specific body condition

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AP Biology

AP Biology

Thermoregulation• Maintain an internal

temperature within a

tolerable range

• Endothermic animals

generate heat by

metabolism (birds and

mammals)

• Ectothermic animals

gain heat from external

sources (invertebrates,

fishes, amphibians, and

nonavian reptiles)AP Biology

AP Biology

• Metabolic rate: total amount of energy an animal uses in a unit of time

• Ectotherms have much lower metabolic rates than endotherms of a comparable size

Energy Use

Metabolic rate is inversely related to body size among similar animals

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Balancing Heat Loss and Gain•Organisms exchange heat by four

physical processes: radiation, evaporation, convection, and

conduction

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Five adaptations for thermoregulation:

• Insulation (skin, feather, fur, blubber)

• Circulatory adaptations (countercurrent exchange)

• Cooling by evaporative heat loss (sweat)

• Behavioral responses (shivering)

• Cellular adjustments (“antifreeze” proteins, membrane lipids, enzyme variants)

AP Biology

Countercurrent

heat exchange

A counterflow mechanism that

enables fluids at different

temperatures flowing in

channels in opposite directions

to exchange their heat content

without mixing.

An example of countercurrent heat

exchange occurs in the feet geese, in

which heat from blood in the arteries

supplying the feet is transferred to blood

returning to the body's core in veins that lie

close to these arteries.

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AP Biology

AP Biology

Controlling Body Temperature

high

low

nerve signals

sweat

nerve signals

brain

body temperature

shiver brain

dilates surfaceblood vessels

constricts surfaceblood vessels

Nervous System Control

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Torpor and Energy Conservation

▪ Torpor is a physiological state in which activity is low and metabolism decreases

▪ Save energy while avoiding difficult and dangerous conditions

▪ Hibernation: torpor during winter cold and food scarcity

▪ Estivation: summer torpor, survive long periods of high temperatures and scarce water

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Osmoregulation

Nitrogenous wastesMarine vs. Freshwater FishAP Biology

Osmoregulation

Mammalian Excretory System

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Osmoregulation

Why do all land animals have to conserve water?

▪ always lose water (breathing & waste)

▪ may lose life while searching for water

▪ Water balance

freshwater

▪ hypotonic

▪ water flow into cells & salt loss

saltwater

▪ hypertonic

▪ water loss from cells

land

▪ dry environment

▪ need to conserve water

▪ may also need to conserve salt

hypotonic

hypertonic

AP Biology

Intracellular Waste

▪ What waste products?

what do we digest our food into…

▪ carbohydrates = CHO

▪ lipids = CHO

▪ proteins = CHON

▪ nucleic acids = CHOPN

CO2 + H2O

NH2 =

ammonia

CO2 + H2O

CO2 + H2O

CO2 + H2O + N

CO2 + H2O + P + N

|

| ||H

HN C–OH

O

R

H

–C–

Animalspoison themselvesfrom the insideby digestingproteins!

lots!verylittle

cellular digestion…cellular waste

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AP Biology

AP Biology

Nitrogenous waste disposal

▪ Ammonia (NH3)

very toxic

▪ carcinogenic

very soluble

▪ easily crosses membranes

must dilute it & get rid of it… fast!

▪ How you get rid of nitrogenous wastes depends on

who you are (evolutionary relationship)

where you live (habitat)

aquatic terrestrial terrestrial egg layer AP Biology

Nitrogen waste▪ Aquatic organisms

can afford to lose water

ammonia

▪ most toxic

▪ Terrestrial need to conserve

water

urea

▪ less toxic

▪ Terrestrial egglayers need to conserve water

need to protectembryo in egg

uric acid

▪ least toxic

AP Biology

Freshwater animals

▪ Water removal & nitrogen waste disposal

remove surplus water

▪ use surplus water to dilute ammonia & excrete it

need to excrete a lot of water so dilute ammonia &

excrete it as very dilute urine

▪ also diffuse ammonia continuously through gills or

through any moist membrane

overcome loss of salts

▪ reabsorb in kidneys or active transport across gills

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Land animals

▪ Nitrogen waste disposal on land

need to conserve water

must process ammonia so less toxic▪ urea = larger molecule = less soluble = less toxic 2NH2 + CO2 = urea

produced in liver

kidney▪ filter solutes out of blood

▪ reabsorb H2O (+ any useful solutes)

▪ excrete waste urine = urea, salts, excess sugar & H2O

urine is very concentrated

concentrated NH3 would be too toxic

OC

HNH

HNH

Ureacosts energyto synthesize,

but it’s worth it!

mammals

AP Biology

Egg-laying land animals

itty bittyliving space!

▪ Nitrogen waste disposal in egg

no place to get rid of waste in egg

need even less soluble molecule

▪ uric acid = BIGGER = less

soluble = less toxic

birds, reptiles, insects

Uric Acid = Polymerized urea

large molecule

precipitates out of solution

▪ doesn’t harm embryo in egg

white dust in egg

▪ adults still excrete N waste as white paste

no liquid waste

uric acid = white bird “poop”!

This is also why male birds don’t have penis

AP Biology

Summary ▪ Not filtered out

cells proteins

remain in blood (too big)

▪ Reabsorbed: active transport

Na+ amino acids

Cl– glucose

▪ Reabsorbed: diffusion

Na+ Cl–

H2O

▪ Excreted

urea

excess H2O excess solutes (glucose, salts)

toxins, drugs, “unknowns”

whyselective reabsorption

& not selectivefiltration?

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AP Biology

AP Biology

Environmental Ques and

Homesostasis

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Daily and Seasonal Timing

Circadian and Circannual Clocks in Living

Things

Many Living Things Have a Internal Clocks

DAILY

Regulates daily cycle of

activitiesRegulates seasonal

changes in gene expression

and behavior

SEASONAL

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Circadian Rhythm are Endogenous

▪ Occur internally- do not require environmental cues

▪ BUT can be altered by environmental cuesAP Biology

Evolutionary Adaptations

▪ Daily and seasonal changes are genetic characteristics

that have evolved because their presence is

advantageous

▪ Natural selection has favored these traits

▪ We have genes that control these rhythms

▪ But environment can change gene expression (epigenetics)

▪ There are clear patterns of brain wave activity, hormone production,

cell regeneration and other biological activities linked to this daily

cycle.

Under Genetic Control

AP Biology

Circadian Rhythms in Plants

▪ Change in leaf

orientation

▪ Opening of

stomata – pores in

the leaf

▪ Opening of flowers

and release of

fragrance

▪ Movement of Leaves happened at nearly same time

every day, even on cloudy days

▪ BUT artificial light at different times confuses the

plant’s internal clockAP Biology

Circadian Rhythm in Animals

Closely tied to sleep-wake cycle

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AP Biology

Why You’re Stressed in the Morning

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Light Might Inhibit Melatonin Release▪ Melatonin to controls sleep urges

▪ artificial lights can prevent melatonin release and keep people

awake

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Seasonal Clocks

Affect gene expression

Control things like:

Shedding of coats

Reproduction

Hibernation

Migration

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In Animals▪ Light absorption by the eye triggers change in gene

expression / Thought to be mediated by melatonin

Shedding of Coats or Changing of Color

Arctic Wolf in SummerArctic Wolf in Winter

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Seasonal

Reproduction

▪ Many species only

reproduce in

spring or summer

▪ When more food

(energy) is

abundant

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Ex. How Seasons Affect Reproduction

in Animals

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AP Biology

Hibernation/Estivation

▪ Helps conserve

energy when little

food available

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Migration▪ Changes in light trigger

hormone changes

As there’s less light

birds build up fat for

journey

▪ Also occurs in birds in

captivity with consistent

light sources

▪ BUT reducing light brings

about changes in behavior