Science and Technology Class 9 Notes Chapter 15 Maharashtra Board

Life Processes in Living Organisms

1. Introduction

Living organisms perform essential processes like transportation, excretion, and coordination to survive. Plants and animals transport nutrients and oxygen to cells, remove waste to stay healthy, and coordinate activities to respond to their environment. These processes ensure the body works smoothly and maintains balance (homeostasis).

2. Transportation in Plants

Definition: Transportation is the movement of substances like water, minerals, and food from one part of a plant to another.

Why Needed: Plants need less energy than animals but require inorganic substances (nitrogen, phosphorus, magnesium) from soil for growth. Unlike animals, plants don’t move, so they rely on specialized tissues.

a. Transportation of Water

Tissues Involved: Xylem conducts water and minerals from roots to leaves.

Mechanisms:

Root Pressure:

• Roots absorb water and minerals from soil due to concentration differences, making root cells turgid.
• Turgid cells create pressure, pushing water into xylem, forming a water column.
• Effective in small plants and shrubs, especially at night.
• Example: Staining a balsam plant’s roots with safranin shows water moving up the stem.

Transpiration Pull:

• Water evaporates from leaves through stomata (pores), controlled by guard cells.
• Evaporation reduces water in leaves, creating a suction (pull) that draws water up from roots via xylem.
• Helps distribute water and minerals and cools the plant.
• Fact: An oak tree releases 151,000 liters of water yearly; a maize crop releases 11,400-15,100 liters daily per acre.

b. Transportation of Food

Tissues Involved: Phloem transports food (e.g., sucrose) from leaves to all plant parts.

Process (Translocation):

• Food moves upward or downward using energy from ATP (active process).
• When food reaches a cell, water enters by diffusion, increasing pressure to push food to nearby cells.
• Excess food is stored in roots, fruits, or seeds.

Example: During flowering, sugar from roots moves to buds, helping flowers bloom.

3. Excretion

Definition: Excretion is the removal of harmful or waste substances from the body to prevent damage.

Importance: Accumulated wastes like urea or ammonia can harm or kill organisms if not removed.

a. Excretion in Plants

Process: Plants lack specific excretory organs, making excretion simpler than in animals.

Methods:

• Gaseous Wastes: Released through stomata by diffusion (e.g., oxygen, water vapor).
• Solid Wastes: Stored in vacuoles of leaves, fruits, or bark, which fall off (e.g., leaf fall in autumn).
• Other Wastes: Stored as resin or gum in old xylem or released into soil via roots.
• Raphides: Needle-shaped calcium oxalate crystals in some plants (e.g., arum leaves) cause irritation to deter herbivores.

Useful Wastes for Humans:

• Latex: Used for rubber (e.g., rubber trees).
• Gum: Used in food and medicine (e.g., acacia gum).
• Resin: Used in varnishes (e.g., pine resin).

b. Excretion in Humans

Excretory System: Includes kidneys, ureters, urinary bladder, and urethra; skin and lungs also help.

Process:

Kidneys: Main excretory organs, located on either side of the spine.

• Contain ~10 lakh nephrons (functional units).
• Each nephron has a Bowman’s capsule with a glomerulus (capillary network).
• Glomerulus filters blood, separating urea and wastes to form urine.
• Useful substances (water, glucose) are reabsorbed; urine collects in the renal pelvis.

Ureters: Carry urine to the bladder.

Urinary Bladder: Stores urine, controlled by nerves for voluntary release.

Urethra: Expels urine from the body.

Other Organs: Skin excretes sweat; lungs release carbon dioxide.

Facts:

• Kidneys filter ~190 liters of blood daily, producing 1-1.9 liters of urine.
• Right kidney is slightly lower than the left.

Dialysis:

• Used when kidneys fail due to injury or infection.
• A machine filters nitrogenous wastes from blood (500 ml at a time), returning purified blood to the body.
• Prevents toxin buildup that could lead to death.

4. Coordination

Definition: Coordination is the process of organizing body activities to work together, responding to internal and external changes.

Importance: Ensures smooth functioning and maintains homeostasis (body balance) for optimal efficiency.

Examples:

• Accidentally biting your tongue while eating shows lack of coordination.
• Players in a game coordinate movements to catch a ball.

a. Coordination in Plants

How It Works: Plants lack a nervous system but use electrochemical impulses and hormones for coordination.

Types of Movements:

• Phototropic: Shoots grow toward light (e.g., sunflowers bend toward sunlight).
• Gravitropic: Roots grow downward (e.g., roots anchor in soil).
• Hydrotropic: Roots grow toward water.
• Chemotropic: Pollen tubes grow toward ovules for fertilization.

Growth-Irrelevant Movements:

• Triggered by stimuli like touch or light, not growth.

Examples:

• Touch-me-not (Mimosa): Leaves fold when touched due to water content changes.
• Venus Flytrap: Trap closes to catch insects, digesting them.
• Lotus: Flowers open in daylight; tuberose opens at night.
• Drosera: Leaf fibrils bend to trap insects.
• Balsam: Fruits burst to disperse seeds.

Hormones Involved:

• Auxin: Promotes cell enlargement in shoots.
• Gibberellins: Aid stem elongation.
• Cytokinins: Support cell division.
• Abscisic Acid: Inhibits growth, causes leaf wilting.

b. Coordination in Humans

Systems Involved:

Nervous System: Uses neurons to transmit fast, short-lived impulses.

Endocrine System: Uses hormones for slow, long-lasting effects.

Nervous Control:

Neurons (Nerve Cells):

• Structure: Dendrites (receive impulses), cell body (processes impulses), axon (sends impulses).
• Synapse: Gap between neurons where neurotransmitters transfer impulses.
• Neuroglia: Support cells for neurons.
• Example: Touching a hot object triggers neurons to signal muscles to withdraw the hand.

Types of Neurons:

• Sensory Neurons: Carry impulses from sensory organs to brain/spinal cord.
• Motor Neurons: Carry impulses from brain/spinal cord to muscles/glands.
• Association Neurons: Integrate signals within the nervous system.

Human Nervous System:

Central Nervous System (CNS): Brain and spinal cord.

• Brain:
  • Cerebrum: Largest part, controls thinking, speech, memory; has convolutions for more neurons.
  • Cerebellum: Manages balance and coordination; has shallow grooves.
  • Medulla Oblongata: Controls vital functions (breathing, heartbeat); connects to spinal cord.
  • Protected by meninges and cerebrospinal fluid in ventricles.
  • Facts: Weighs 1300-1400 g, has ~100 billion neurons; left brain (logic) controls right body, right brain (creativity) controls left.

Spinal Cord: Protected by vertebral column, relays impulses; ends in filum terminale.

Peripheral Nervous System (PNS):

• Cranial Nerves: 12 pairs from brain, control head and thorax.
• Spinal Nerves: 31 pairs from spinal cord, control arms, legs, skin.

Autonomic Nervous System: Controls involuntary organs (heart, lungs).

Reflex Action:

• Immediate, involuntary response to a stimulus (e.g., blinking at an approaching object).
• Involves a reflex arc: sensory neuron → spinal cord → motor neuron, bypassing the brain.
• Example: Pulling hand from a hot surface protects from burns.

Chemical Control:

Endocrine Glands: Ductless glands release hormones into blood.

Hormones: Regulate growth, metabolism, stress response.

Examples:

• Insulin (Pancreas): Lowers blood sugar when high.
• Thyroxine (Thyroid): Controls metabolism.
• Adrenaline (Adrenal): Prepares body for stress.

Hormones act slowly but have long-lasting effects, complementing the fast nervous system.