Plant and Animal Response to Stimuli

Chemical and Nervous Control

• Process comparison in plants and animals.

Learning Objectives

• Ability to explain how plants and animals respond to environmental stimuli
• Ability to describe the mechanisms of chemical control in plants and animals

Introduction (Plant)

• Plants respond to environmental cues like light and chemical signals.
• Plants physiological and morphological features change in response to environmental cues.

Plant Response

• All living things respond primarily to survive environmental stimuli
• Mimosa pudica's common name is Makahiya
• Helianthus annuus scientific name is Sunflower
• Stomata closes to prevent rapid water loss.
• Banksias need fire to germinate; bushfires cause the follicles to open
• Plants release chemicals for defense against pathogens, predators, and nearby plants against impending attacks.

Tropism

• A biological mechanism enables plant movements toward/against a stimulus.
• Roots usually grow underground moving toward water and the center of gravity.
• Leaves usually grow above ground where they absorb sunlight.
• Plants respond to external stimuli through tropism.
• Tropism is movement caused by change in plant growth pattern.
• Tropism can be negative or positive, depending if the plant moves towards, or away from the stimulus.

Geotropism

• Gravity causes a response in plants growth.

Hydrotropism

• The way a plant grows or bends in response to water.

Thigmotropism

• It happens when plants bend or grow from a touch.
• An example would be when vines wrap around an arbor frame

Phototropism

• The way a plant grows or bends in response to light.

Hormones

• Chemical messengers in plants.
• They regulate various biochemical and physiological responses:
  • Seed germination
  • Flowering
  • Photosynthesis
  • Fruit ripening
  • Shoot and root development.

Plant Hormone: Auxin

• Produced in embryo of seed, meristems of apical buds, and young leaves
• Functions include:
  • Stimulates stem elongation, root growth, cell differentiation, and branching.
  • Regulates fruit development
  • Enhances apical dominance
  • Functions in phototropism and gravitropism
  • Promotes xylem differentiation
  • Retards leaf abscission

Plant Hormone: Gibberellins

• Produced in meristems of apical buds and roots, young leaves, and embryo.
• Functions include:
  • Promote seed and bud germination
  • Stem elongation
  • Leaf growth
  • Stimulates flowering
  • Development of fruit
  • Affects root growth and differentiation

Plant Hormone: Cytokinins

• Synthesized in roots and transported to other organs
• Functions include:
  • Stimulates stem elongation, root growth, cell differentiation, and branching, Regulates fruit development, enhances apical dominance
  • Functions in phototropism and gravitropism
  • Promotes xylem differentiation
  • Retards leaf abscission

Plant Hormone: Brassinosteroids

• Produced in seeds, fruits, shoots, leaves, and floral buds
• Functions include:
  • Inhibit root growth
  • Retard leaf abscission
  • Promote xylem differentiation

Plant Hormone: Abscisic Acid

• Produced in leaves, stems, roots, and green fruit
• Functions include:
  • Inhibits growth
  • Closes stomata during water stress
  • Promotes seed dormancy

Plant Hormone: Ethylene

• Produced in the tissues of ripening fruit, nodes of stems, aging leaves and flowers
• Functions include:
  • Promotes fruit ripening
  • Opposes some auxin effects
  • Promotes or inhibits growth and development of roots, leaves, and flower depending on species.

Animals Chemical and Nervous Control

• Chemical control is regulated by the endocrine system, including hormones
• Nervous control is regulated by the nervous system with neuronal mechanisms

Learning Objectives

• Ability to explain how animals respond to environmental stimuli.
• Ability to describe the mechanisms of chemical and nervous control in animals.

Introduction

• Chemical control utilizes the endocrine system/hormones, is slow-acting, and its effects are long-term.
• Nervous control uses the nervous system/neuronal mechanisms, is fast-acting and its effects are short-term, though frequent stimulation creates longer behavioral responses.

Nervous System

• It is responsible for coordinating the functions of the other body systems.

Principal functions

• Sensory input comes from sensory receptors.
• Integration decides what actions should take place.
• The nervous system activates parts of the body for motor output.

Divisions of the Nervous System

• Central Nervous System (CNS).
• Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Composed of the brain and the spinal cord.
• The Brain is the main control center
• The spinal cord connects the brain to other nerves of the body

Peripheral Nervous System (PNS)

• Composed of nerves that branch out from the brain and spinal cord
• These branch out to specific parts of the body
• Divided into the somatic and autonomic nervous system
• The somatic system controls voluntary movement
• The autonomic system controls involuntary actions

Neuron

• The basic and functional unit of the nervous system.

Nervous Tissue: Neuroglia or Glial Cells

• They surround and protect the neurons.

Nervous Tissue: Astrocytes

• Found in CNS.
• They are the most abundant, and anchor neurons to blood supply.
• They govern the exchange of materials between neurons and capillaries.

Nervous Tissue: Microglial Cells

• Found in CNS.
• They are protective microglial cells, and act as the main source of immune defense against invading microorganisms in the brain and spinal cord.

Nervous Tissue: Ependymal Cells

• They line cavities in the brain and spinal cord.
• They create, secrete, and circulate cerebrospinal fluid, cushioning those cavities/organs

Nervous Tissue: Oligodendrocytes

• Wrap around neurons, producing an insulating barrier called the myelin sheath.

Peripheral Nervous System: Glial Cells

• Include Satellite Cells and Schwann cells.
• Satellite Cells surround and support neuron cell bodies.
• Schwann cells produce an insulating barrier called the myelin sheath.

Three Common Things of Neurons

• Neurons are some of the longest-lived cells
• Neurons are irreplaceable (amitotic).
• Neurons have huge appetites, so a high metabolic rate.

Neurons: Basic Structures

• Soma/Cell Body: It contains nucleus, and neurons life support
• Dendrites: Pick up messages from other cells and convey information to the cell body.
• Axon: Transits electrical impulses away from the cell body to other cells.

Neuron Impulse Travel

• Sensory (Afferent) Neurons pick up messages and transit impulses from sensory receptors, sending them toward the CNS
• Motor (Efferent) Neurons transit impulses away from the CNS and out to the body's muscles/glands
• Interneurons (Association) Neurons live in the CNS, transiting impulses between sensory and motor neurons.