Biology Plant Responses and Endocrine System

Geotropism: Growth in response to gravity. Roots exhibit positive geotropism (grow towards gravity), while shoots display negative geotropism (grow away from gravity).
Phototropism: Growth in response to light. Stems exhibit positive phototropism (grow towards light), while roots demonstrate negative phototropism (grow away from light).
Hydrotropism: Growth in response to water or moisture. Roots exhibit positive hydrotropism (grow towards water).
Chemotropism: Growth in response to chemical stimuli. An example is the growth of the pollen tube towards the ovule, which is a positive chemotropism.
Thigmotropism: Growth in response to touch. Tendrils wrapping around a support is an example of positive thigmotropism.

Exocrine glands: Release secretions through ducts onto an epithelial surface.
Endocrine glands: Ductless glands that release hormones directly into the bloodstream. Examples include the pituitary, thyroid, adrenal, pineal, pancreas, ovary (female), and testis (male).

The nervous system is the body's control center, made up of nervous tissue.
Neurons: Basic structural and functional units of the nervous system. Responsible for transmitting nerve impulses.
Neuron structure:
- Cell body (soma): Contains the nucleus and other organelles. Maintains the cell's functions.
- Dendrites: Branching structures that receive signals from other neurons and transmit them towards the cell body.
- Axon: Long, thread-like structure that carries impulses away from the cell body. Ends in axon terminals, which transmit signals to other neurons, muscles, or glands.
- Myelin sheath: Insulates the axon and speeds up nerve impulse transmission.
Working of a neuron:
- Stimulus received: The neuron receives a stimulus that initiates an electrical signal called an action potential.
- Impulse generation: The action potential is generated at the cell body and travels along the axon.
- Impulse propagation: The nerve impulse moves down the axon towards the axon terminals.
- Synapse transmission: Neurotransmitters are released at the synapse to transmit the signal to the next neuron or target cell.
- Response: The signal leads to a response, such as muscle contraction or hormone release.

Consists of the brain and spinal cord.
The brain controls bodily functions, while the spinal cord relays signals between the brain and the peripheral nervous system.

Serves as the central coordination hub of the body, enabling thinking and action.
Regions of the Brain:
- Forebrain: Composed of the cerebrum.
- Midbrain: Composed of the hypothalamus.
- Hindbrain: Composed of the cerebellum, pons, and medulla oblongata.

The largest brain region responsible for receiving sensory impulses.
Cerebrum: The uppermost structure of the brain, responsible for thinking, reasoning, speech, information processing, voluntary motor actions, sensory perceptions, learning, and memory.
Lobes:
- Frontal: Controls voluntary muscle movements, memory, and speech.
- Parietal: Responsible for touch and taste.
- Temporal: Responsible for smell and hearing.
- Occipital: Responsible for vision.

Contains the hypothalamus.
Hypothalamus: Located at the base of the cerebrum. Controls eating, drinking, sleep, and wake cycles.
Pituitary gland: Pea-sized gland situated at the base of the brain. Functions as the master gland, overseeing the secretions of all other endocrine glands. Produces Growth Hormone (GH), LH, and FSH.
- Insufficient GH secretion: Results in dwarfism.
- Excessive GH secretion: Leads to gigantism in children and acromegaly in adults.

Leaf-like gland located behind the stomach.
Functions as both an endocrine and exocrine gland.
Endocrine function: Produces insulin and glucagon, which act antagonistically to regulate blood sugar levels.
Exocrine function: Secretes enzymes to break down proteins, lipids, carbohydrates, and nucleic acids in food.
Insufficient insulin production: Results in diabetes.

Gamete-producing organs.
Testes (male): Produce androgen (testosterone and other male hormones).
Ovaries (female): Produce estrogen and progesterone (female hormones).
Androgen and estrogen: Contribute to gamete production and influence the sexual characteristics of males and females, respectively.
Progesterone: Functions as the pregnancy hormone.

Contain special proteins that change their shape and arrangement in response to electrical impulses, causing the muscle to shorten or contract.

Chemical substances secreted in trace amounts by specialized tissue called endocrine glands.
Example: Thyroxin hormone, produced by the thyroid gland, regulates metabolism of carbohydrates, fats, and proteins.

Hormone synthesized at the shoot tips.
Helps plants respond to light by stimulating cell elongation on the shady side of the shoot, causing the plant to bend towards the light.