Unit 5 L1 Homeostasis & Behavior stimulus A stimulus is anything that causes a reaction or change in an organism. response A response is an organism’s reaction to a stimulus. These can be internal or external behavior A set of actions taken by an organism in response to a stimulus is called a behavior.

Some animals respond to cold temperatures by growing extra fur to stay warm, while others respond by moving to warmer environments. Arctic Fox Barn swallow

Even though an organism’s outside environment may change, conditions inside its body must stay relatively constant. Homeostasis is maintaining a stable balance in the body. Organisms’ bodies constantly respond to stimuli to maintain homeostasis.

How are stimuli detected? Multicellular organisms have sensory cells in their bodies that detect specific stimuli. Sensory receptors are found in sensory organs. Examples: eyes, nose, skin, whiskers, and ears.

Where do responses come from? When an animal’s sensory receptors detect stimuli, they send messages along the nervous system (electrical). Even plants have an electrical message system. Responses are also caused by hormones (chemical signals) An organism’s response is usually the result of the action of both hormones and electrical signals.

What is an external stimulus? Comes from outside the body of an organism and that influences the behavior of the organism. Examples: temperature, sound, light, Taxis Taxis is the movement of organisms toward or away from an external stimulus. Positive taxis = moving toward an external stimuli Negative taxis = moving away from an external stimuli

Positive Taxis Moving towards a watering hole Moving towards a food source

Negative Taxis Moving away from a threatening situation

Responding to External Stimuli External stimuli are things that cause a reaction from outside the body (ex) bats use sound wave reflection called echolocation, to find their prey

Tropism is the movement of a plant in response to an external stimulus. Plant Tropisms:Phototropism Thigmotropism Hydrotropism Geotropism/Gravitropism

Phototropismmovement or growth in response to light(s)

Thigmotropismmovement or growth in response to touch or contacttendrils

Hydrotropismmovement or growth in response to water Porous pot

Geotropism/Gravitropismmovement or growth in response to gravity Negative gravitropism

What is an internal stimulus? A stimulus that comes from inside an organism’s body Examples: hunger thirst getting sick insect metamorphosis or puberty water pressure in plants growing

A cicada hatching is caused by an internal stimuli (hormones) Metamorphism

Tiny pores (stomata) in the plant’s leaves are open to let C0₂ in and O₂ out but water vapor is escapes If the plant loses too much water the guard cells close to prevent further water loss

Water pressure within plant cells helps the plant to remain upright.

How does homeostasis work? To maintain homeostasis, organisms must constantly respond to external and internal stimuli. An organism may not be aware of these responses, such as a change in blood pressure or the filtering of wastes by the kidneys. Homeostatic responses allow individual cells and complete body systems to function properly. Many homeostatic processes are controlled by hormones.

What are some behaviors that improve survival? Fight-or-Flight response Finding a space to live (territory) A space to live includes:Food Water Potential mates Help raising young

Fight-or-Flight Response When faced with a threatening stimulus such as a predator or natural disaster, organisms display the fight- or-flight response. Effects: an increased heart rate, anxiety, decreased blood supply to certain muscles, and a release of hormones and other chemicals in the body. These changes give the body a burst of energy and strength, which allow an organism to physically fight or run away in times of danger.

Is Behavior Innate or Learned? Innate behavior is influenced by genes (DNA) Ex: ability to walk, bees tend to fly, ducks/whales can swim (at birth), earthworms dig tunnels, puppies chew on things, birds sing (when nearly grown)

Learned behaviors are behaviors learned through experience or from watching other animals Ex: language for humans is innate but speaking a specific language is learned Wolves learn to hunt by watching adults

Other examples of reacting to external stimuli Communication This marks territory, share resources, find family and mates, scare off predators

Biological Clock Internal control of natural cycles Ex: when to store food when to fly south for the winter

Circadian Rhythms Part of the biological clock but is concerned with very small amounts of time, usually daily cycles Ex: bats are awakened by their circadian rhythms every night

2. Migration (seasonal) When food is scarce because of winter or dry weather, many animals migrate

Snow Geese Population ≈ 5 million

Snow Geese Migration Map

3. Hibernation (seasonal) Occurs during winter when food is scarce These animals lower their body temperature and heart rate and use stored fat for energy Black bears hibernating

4. Estivation (seasonal) Occurs during the dry or hot summer months when water and food are scarce It is like hibernating but during the summer California ground squirrels estivate during the hot summer

What behaviors help plants survive environmental changes? Food Storage Water storage Dormancy

Food Storage Due to seasonal changes many plants store extra food in bulbs(short stem) or tubers (roots) Examples: Onions Potatoes Carrots

Water Storage Most tropical rainforest plants have large leaves (capture more light) and thin cuticles (waxy covering to prevent water loss) However in desert climates water is scarce so plants have some very unique adaptations

saguaro cactus Cacti store extra water in their stems They do not have leaves because they lose a lot of water They have chloroplast in their stems for photosynthesis

They have thick cuticles to prevent water loss Spines prevent animals from eating them

Roots are shallow to absorb as much water as they can when it rains Rain may come once or twice a year and only percolates down several inches in most cases

Plant Dormancy During dormancy, a plant conserves energy and stops growing Helps plants to survive during harsh conditions such as cold winter months or hot summers. many plants store energy in bulbs or roots before entering dormancy