Plant Hormones and Growth

• As the complexity of organisms increases, the distance between cells and organs also increases.
• This necessitates a system for different parts to function as a single unit through coordination.
• To pick up an object, coordination between eyes, hands, legs, and the vertebral column is needed.
• This ensures actions follow a sequence.
• A similar mechanism is necessary for internal bodily functions.
• Changes in the environment organisms respond to are called stimuli
• An organism's reaction or response to a stimulus is usually movement of a body part
• Maintenance of constant internal conditions is called homeostasis.
• Homeostasis comes from 'homeo' same and 'stasis' standing still.
• Plants, like animals, must control and coordinate their functions, though they lack a nervous system.

Coordination in Plants

• Plants use chemical messengers, plant hormones called phytohormones, for control and coordination, since they do not have a nervous system
• Plant growth occurs in three stages: cell division, cell enlargement, and cell differentiation.
• Plant hormones control these three stages of plant growth
• Plant hormones also control dormancy, stomata, leaf fall, fruit growth, ripening, and aging.
• There are four main plant hormones: auxins, gibberellins, cytokinins, abscisic acid, and ethylene gas.
• Auxins, gibberellins, and cytokinins promote plant growth.
• Abscisic acid inhibits plant growth.

Auxins

• Promotes cell enlargement and differentiation in plants.
• Promotes fruit growth.
• Responsible for phototropic and geotropic movements.
• Auxins are made at the tips of stems and roots.
• Auxin travels away from light and towards gravity.
• In stems, auxin speeds up growth.
• In roots, auxin slows down growth.
• Synthetic auxins like indole -3- acetic acid and 2,4-D are used in agriculture and horticulture.
• Gibberellins promote cell enlargement and differentiation when auxins are present
• Gibberellins helps in stem elongation, breaking dormancy in seeds and buds, and stimulating germination.
• Gibberellins also promotes fruit growth
• Gibberellic acid (GA3) can be sprayed on grape vines to induce parthenocarpy (seedless grapes).
• Cytokinins promote cell division in plants.
• They help disrupt seed and bud dormancy.
• They also delay leaf aging, stimulate stomata opening, and promote fruit growth.
• Abscisic acid functions mainly as a growth inhibitor.
• It encourages seed and bud dormancy and stomata closing.
• ABA promotes leaf wilting and shedding and causes flower and fruit detachment.
• Ethylene gas is a plant hormone that stimulates fruit ripening
• Raw fruit ripens faster when kept with a ripening fruit because of the ethylene gas released.
• Calcium carbide produces acetylene gas when it meets or reacts with water which is used to ripen fruits quickly.

Plant Movements

• Plant movements are divided into tropic and nastic movements.
• Geotropic movement is growth in response to gravity.
• Roots show positive geotropism, growing in the direction of gravity.
• Stems show negative geotropism, which means that they grow against the direction of gravity.
• Phototropic movement is growth in response to light.
• Stems show positive phototropism.
• Roots show negative phototropism.
• Stems bend toward sunlight due to a higher cell division rate on the side away from the light.
• The heightened cell division rate is attained by increased secretion of the plant hormone auxin.
• Hydrotropic movement happens when roots grow towards a water source in the soil, which is a positive hydrotropic movement.
• Thigmotropic movement occurs when a plant grows in response to touch.
• Tendrils of climbers show such movement, coiling around a support due to differential cell division caused by auxin.
• Chemotropic movement is when a plant part moves in response to a chemical stimulus.
• Positive chemotropism is growth towards the chemical.
• Negative chemotropism is growth away from the chemical.
• Pollen tube growth towards the ovule is positive chemotropism, guided by a sugary substance.
• Nastic movements do not depend on stimulus direction.
• Seismonastic or thigmonastic movements are brought about by mechanical stimuli like contact.
• Example: Mimosa pudica leaves droop when touched, which occurs due to the change of water balance causing the cells to lose water and become flaccid.
• Photonastic movements are induced by light intensity changes.
• Flowers open and close with increasing and decreasing light intensity changes.
• Thermonastic movements are caused by temperature changes.
• Mirabilis jalapa blooms in the late afternoon and closes by mid-morning.
• Tulip flowers bloom as the temperature rises.
• Nyctinastic Movements are commonly called ‘sleeping movements' from light and temperature stimuli, with leaves drooping at night and rising again in the morning.

Control and Coordination in Animals

• In animals, the nervous and endocrine systems are responsible for control and coordination.

The Nervous System

• The main component of the nervous system is nervous tissue.
• The nerve cell or neuron is the functional unit of the nervous system.
• It is mainly responsible for control and coordination in animals.
• Receptors are specialized nerve fiber tips that collect information.
• Receptors are in the sense organs of animals.
• Phono-receptors are in the inner ear and are for hearing and balance.
• Photo-receptors in the eye are responsible for visual stimulus.
• Thermo-receptors in the skin detect pain, touch, and heat.
• Olfactory-receptors in the nose receive smells.
• Gustatory-receptors in the tongue help in taste detection.
• The receptors receive stimuli and send messages as electrical impulses through sensory nerves to the spinal cord and brain.
• An effector is a body part, like muscles or glands, that responds to a stimulus based on instructions from the nervous system.

Neuron

• A neuron is the structural and functional unit of the nervous system.
• A neuron has three main parts: dendrites, cyton/soma/cell body, and axon.
• Dendrites receive impulses from other neurons.
• The cyton/soma processes impulses.
• Axons transmit impulses to other neurons, muscles, or glands.
• Axons can be myelinated or non-myelinated.
• Impulse transmission is faster in myelinated neurons.
• Schwann cells and the myelin sheath provide myelin insulation to axons in the peripheral nervous system and increase impulse speed.
• Node of Ranvier are gaps (about 1 micrometer in diameter) formed between myelin sheath cells along axons or nerve fibers.

Types of Neurons

• Sensory neurons receive signals from a sense organ.
• Motor neurons send signals to a muscle or gland.
• Association or relay neurons relay signals between sensory and motor neurons.
• A synapse is the contact point between an axon's terminal branches and another neuron's dendrite.
• Neuromuscular Junction (NMJ) is the point where a muscle fiber meets a motor neuron carrying nerve impulse from the central nervous system.
• Nerve impulses travel from dendrites to the cell body, then along the axon to nerve endings, across a synapse, and to the next neuron's dendrites.
• Chemicals released from an axon tip cross the synapse or NMJ to reach the next cell: Acetylcholine is one such neurotransmitter.

Organs of the Human Nervous System

• The central nervous system includes the brain and spinal cord.
• The brain controls bodily functions.
• The spinal cord relays signals between the brain and the peripheral nervous system.
• The peripheral nervous system includes cranial and spinal nerves.
• There are 12 pairs of cranial nerves.
• Cranial nerves emerge from the brain and go to organs in the head.
• There are 31 pairs of spinal nerves that emerges from the spinal cord and go to all organs below the head areas.
• Visceral nerves connect internal organs to the spinal cord and brain.
• The autonomous nervous system consists of a chain of nerve ganglia along the spinal cord and controls involuntary actions
• It divides into sympathetic and parasympathetic nervous systems.
• The sympathetic nervous system (SNS) controls the 'fight or flight' response, preparing us to face danger by directing energy to survival functions.
• The hormone adrenaline is released from the adrenal gland which causes physiological changes to prepare one to either flight or flee.
• Adrenaline increases heart rate and blood pressure, boosting oxygenated blood flow to muscles.
• The bronchial tubes dilate, increasing airflow to the lungs and oxygen to the brain, while pupils dilate to improve vision.
• All these responses happen quickly and involuntarily in response to the perceived threat.

Key Effects of the Sympathetic Nervous System

• Adrenaline release
• Increased heart rate
• Increased blood pressure
• Dilation of bronchial tubes
• Glycogen converts to glucose
• Pupils dilate
• Muscles contract
• Saliva production decreases
• Mucus production decreases
• Urine secretion decreases
• Activity in the stomach decreases
• Motility of the large and small intestine decreases

Parasympathetic Nervous System

• Slows down organ activity, inducing a calming effect.
• Breathing and heart rate slows down during sleep.
• Facilitates energy conservation by maintaining steady heart rate and blood pressure, also stimulating digestion and sexual function.
• Includes saliva production, tears, urination, digestion, defecation, and sexual arousal.

Key Effects of the Parasympathetic Nervous System

• Saliva production increases
• Mucus production increases
• Motility of the large and small intestines increases
• Activity in the stomach increases
• Urine secretion increases
• Bronchial muscles contract
• Pupils are constricted
• Heart rate is decreased

Human Brain

• Is a complex organ made of nervous tissue.
• Its tissues are folded to maximize the surface area.
• The brain is protected by three-layered membranes called meninges.
• Cerebrospinal fluid (CSF) cushions the brain against mechanical shocks.
• The brain can be divided into forebrain, midbrain, and hindbrain.

Parts of Forebrain

• Made of the olfactory lobes
• Cerebrum
• Diencephalon

Parts of the Midbrain

• Hypothalamus

Parts of Hindbrain

• Cerebellum
• Pons
• Medulla oblongata

Olfactory Lobes

• Concerned with the sense of smell

Cerebrum

• Is the brain's largest part.
• Divided into right and left hemispheres.
• The two hemispheres are connected by the corpus callosum, which transmits messages from one side to the other.
• Each hemisphere controls the opposite side of the body.
• The cerebral hemisphere is hollow, with an outer cortex (grey colored cell bodies) and inner medulla (axons of neurons- white matter).
• Each hemisphere consists of 4 lobes: Frontal lobe, Parietal lobe, Occipital lobe, and Temporal lobe

Lobes of the Cerebrum

• Frontal Lobe: Reasoning, planning, speech, movement, emotions, and problem solving
• Parietal Lobe: Movement, Orientation, and Recognition
• Occipital Lobe: Visual processing
• Temporal Lobe: Auditory perception, memory, and speech

Functions of the Cerebrum

• Controls voluntary motor actions.
• Serves as the site for sensory perceptions, such as tactile and auditory.
• Seat of learning and memory

Diencephalon

• Lies between the cerebrum and midbrain.
• It is a link between the nervous system and the endocrine System.
• Receives and interprets the signals and the pituitary glands responds by secreting hormones
• Is made of the Thalamas and Hypothalmus

Thalamus

• Relay center for pain and pressure

Hypothalamus

• Lies at the base of the cerebrum.
• Controls the sleep and wake cycle (circadian rhythm).
• Controls urges for eating and drinking, body temperature, the pituitary gland and blood pressure.
• The midbrain connects the forebrain and hindbrain which is found at the top of the brainstem, under the cerebellum.
• Its primary function is relaying transmissions for the central nervous system.
• The midbrain integrates sensory information from the eyes and ears with muscle movements.
• It enables the body to make fine adjustments to movements.
• The hindbrain is made of the pons, medulla oblongata, and cerebellum.
• These structures govern autonomic body systems, controlling breathing, heart rate, sleep, bladder function, equilibrium, and fine motor control.

Pons

• Relays impulses between the cerebellum, spinal cord, and other parts of the brains.
• It regulates respiration.

Medulla

• Forms the brain stem with the pons.
• Lies at the base of the brains and continues into the spinal cord.
• The medulla controls involuntary functions, such as heart beat, respiration, blood pressure, salivation, and vomiting.

Cerebellum

• Is positioned behind the midbrain and brainstem, under the cerebral lobes.
• Coordinates motor functions, posture, and balance.
• Achieves pedaling and steering when riding a bicycle.
• Controls voluntary actions

Spinal Cord

• Is a part of the central nervous system
• Is a long pipe-like structure which arises from the medulla oblongata, part of the brain which consists of a collection of nerve fibres, running through the vertebral column of the backbone.
• Cross-section displays grey matter shaped like a butterfly and is surrounded by white matter
• The grey matter consists of the central canal, which is filled with cerebrospinal fluid (CSF).
• The white matter assists in communication between different CNS layers

Functions of the Spinal Cord

• Forms a connecting link between the brain and the PNS.
• Provides structural support for the body and builds a body posture.
• Facilitates flexible movements.
• Myelin acts as an electrical insulation.
• Communicates messages from the brain to different body parts.
• Coordinates reflexes.
• Receives and processes sensory information which are sent to the brain.

Reflex Action

• Is a special case of involuntary movement in times of immediate danger.
• The limb is immediately pulled away to save itself from danger
• Reflex arc is the path that nerve signals travel to, in a reflex arc, the signal flows in the following directions to illicit a response: Receptor → Sensory neuron → Relay neuron → Motor neuron → Effector (muscle).
• The receptor organ is one at risk of danger.
• The sensory neurons pick up the signal and transfers it to the relay neuron to illicit a motor response

Spinal Cord Processing

• The spinal cord processes the signal and elicits a response
• Signals of reflex arcs will meet at the level of the spinal cord for faster processing and response
• Every reflex activity and action is eventually still controlled directly by the brain

Protection of the Brain and Spinal Cord

• The brain is protected by a fluid-filled balloon which acts as a shock absorber in the cranium (Brain box)
• The spinal cord is protected by the vertebral column
• Muscle tissues have actin and myosin filament
• When a muscle receive nerve signal, a series of reactions and activities begin, that contract a certain muscle.
• Calcium ions enter the cell and cause actin and myosin filaments to be triggered.

Endocrine System

• Is composed of many glands
• A ductless gland is an endocrine gland
• Ductless glands secrete their products directly into the blood stream
• Hormones are produced in the endocrine glands
• Hormones are mainly composed of proteins
• Hormones assist the nervous system in control and coordination
• Nervous system actions occur in every part of the body whereas hormones are needed to elicit a response for control and coordination in some smaller parts of the body.
• Moreover, nervous system functions occur fast whereas hormone activity occurs slower

Hormones

• Chemical messengers which are secreted by specialized tissues called ductless glands or endocrine glands to the the blood stream
• Travel and stimulate or inhibit specific physiological processes to tissues or organs away from their sources
• Target cells have specific receptors or protein molecules on surfaces to be able to recognize and pick up hormones when they arrive
• There are about 20 major hormones in animals which are released by the glands which serve important physiological purposes
• Hormone level can be affected by stress, infection, minerals, and other environmental situations that affect the body

Gland

• Made of tissues, cells, and/or organs
• It is used to secrete a useful chemical compund for a specific function
• Endocrine glands are ductless glands that secrete hormones into the bloodstream
• Pituitary, thyroid, adrenal, and parathyroid are some examples

Exocrine Glands

• An exocrine gland either secretes directly or by ducts onto the skin.
• Examples: Salivary glands through ducts into the mouth to moisten (begins digestion process)
• Exocrine examples are also tears, sweat, gastric glands, the liver, etc
• Heterocrine glands have both endocrine and exocrine glands
• The endocrine glands creates pancreas
• The endocrine part of the pancreas is called Islets of Langerhans which has Alpha cells that secrete glucacon while beta cells secrete insulin to perform exocrine function
• Gonads are heterocrine in nature

Hypothalamus

• Is a minute region, almost the size of an almond, present at the center of the human brains near the pituitary gland
• It is a critical link between the nervous and pituitary gland in a special area
• It maintains steady homeostasis
• Connects the nervous and endocrine systems to control the release of 8 major hormones by the pituiary gland
• The hypothalamus promotes and inhibits activities to maintain homeostasis
• Regulates heart rate, blood pressure, sleep, appetite, body weight, etc
• Controls circadian rhythm of the body

Pituitary

• Located in the base of the brain
• Controls secretions of other endocrine glands and regulates metabolism
• If under-secretes the growth hormones, will cause Dwarfism
• If it over-secretes the growth hormone, it will cause Gigantism for children and acromegaly in adults
• Some hormones that can be released are Thyroid Hormone, Melanocytes Hormone, and Follicle Stimulating Hormone

Thyroid

• Located in the throat and shaped like a butterly
• Releases Thyroxine for body metabolism
• Plays roles in bone growth, nervous system activities, and development in children
• Iodine is required to synthesize thyroxin
• Iodine defiency can cause under-secretion of thyroxin and leads to goiter in adults
• Cretinism is the complete suppression of the mental and physical growth of a child
• Parathyroid glands regulates the calcium and phosphorus levels in the bone

Pineal Gland

• Produces melatonin to regulate sleep patterns

Pancreas

• Located behind the stomach in the abdomen
• Regulate sugar level in the blood
• Insufficent amount of insulin can cause diabetes

Adrenal Gland

• Occurs in pairs in each kidney
• Decreases in size with age
• This gland releases adreanaline or epeinephrine to help with flight and fight
• Cortisol is also found in the gland which has anti-inflammatory properties which can aid the immune system
• They can help regulate metabolism and blood pressure

Epinephrine

• Is also called adrenaline, this hormone responds to increase heart rate, cardiac muscle contractions, blood pressure, etc
• Norepinephrine helps with the reaction to stress.
• Its main role to mobilize the human brains and body for action.
• Epeinephrine and Norepinephrine is stimulated by neuro impulses which come from the nervous system

Thymus

• Is positioned inbetween the two lungs behind the sternum
• Thymosin is a hormone which is used for the immune system purposes
• It will slowly start to reduce in size and replace with body fat.

Gonads

• These are gamete products which testes found it male whereases females have ovaries
• Males can make the hormone testterone whereasse the females produce estrogen and progesterone to helo for sexual purposes
• Testterone works for producing sperm were estrogen and progesterone
• Progesterone is used for preganancy purposes
• Hormone deficiencies and extra will affect the body
• The body has its own feedback tool built-in
• Eat carbohydrate rich meal and the sugar level will reach
• It will be detected by the cells of the pancreas to secret more insulin to create blood and energy in the body to then send to the hormone receptor cells

Explore plant hormones like auxin, gibberellins, abscisic acid, and ethylene, and their roles in growth, dormancy, and responses to stimuli such as light. Understand how these hormones affect stem and root development. Fruit ripening and stomata closing are also covered.