Understanding how similar cells work together as a team
A tissue is a group of similar cells that work together to perform a specific function.
Imagine a cricket team! Just like 11 players work together to win a match, many similar cells work together as a tissue to do a particular job. For example, muscle cells group together to form muscle tissue that helps you move!
In multicellular organisms, different tissues perform different functions. This is called division of labor. It makes the organism more efficient - just like in a factory where different workers do different jobs!
Plant tissues are divided into two main types: Meristematic Tissue and Permanent Tissue.
Meristematic tissue consists of cells that can divide and form new cells. These are found in the growing regions of plants.
Think of meristematic cells as "baby cells" or "growth cells"! They're like kids who keep growing. These cells are found where the plant is growing - tips of roots and shoots. That's why plants grow taller from top and roots grow deeper!
1. Apical Meristem: Found at tips of roots and
shoots. Helps in increasing length (height of plant).
2. Lateral Meristem: Found on sides of stem and
roots. Helps in increasing thickness (girth of plant).
3. Intercalary Meristem: Found between mature
tissues, like at base of leaves. Helps in growth of leaves and
internodes.
Permanent tissue consists of cells that have stopped dividing. They have attained a definite shape, size, and function. They are formed from meristematic tissue.
If meristematic cells are like kids who keep growing, permanent tissue cells are like adults who have stopped growing and now do specific jobs! Once they mature, they specialize in particular tasks.
Permanent tissues are of two types: Simple Permanent Tissue and Complex Permanent Tissue.
Made up of only one type of cells.
1. Parenchyma:
• Most common plant tissue
• Cells are living, thin-walled, and loosely packed
• Have large intercellular spaces
• Store food, provide support
• In leaves, they contain chloroplasts and perform photosynthesis
(called chlorenchyma)
• In aquatic plants, they have air cavities for floating (called
aerenchyma)
2. Collenchyma:
• Cells are living with thickened corners
• Provide mechanical support and flexibility
• Found in leaf stalks, below the epidermis
• Allow bending without breaking (like a rubber band)
3. Sclerenchyma:
• Cells are dead with very thick walls (due to lignin)
• Provide strength and hardness
• Found in stems, around vascular bundles, in seed coats, nut
shells
• Make plant parts hard and stiff
The hard coconut shell is made of sclerenchyma tissue! That's why it's so hard and tough. Similarly, the gritty texture you feel when eating pears is due to sclerenchyma cells called stone cells!
Made up of more than one type of cells working together.
1. Xylem:
• Conducts water and minerals from roots to other parts
• Made of 4 types of cells: Tracheids, Vessels, Xylem parenchyma,
Xylem fibers
• Tracheids and vessels are tubular and dead
• Water moves upward through these tubes
• Also provides mechanical support
2. Phloem:
• Transports food (prepared in leaves) to all parts of plant
• Made of 4 types of cells: Sieve tubes, Companion cells, Phloem
parenchyma, Phloem fibers
• Sieve tubes are living (no nucleus) with perforated walls
• Companion cells help sieve tubes
• Food can move both upward and downward
Think of xylem and phloem as the plant's plumbing system!
• Xylem is like water pipes bringing water from
underground tank (roots) to all floors (parts)
• Phloem is like delivery trucks transporting
food from kitchen (leaves) to all rooms (parts)
Together, they're called vascular tissue - the plant's transport
system!
• Single layer of cells covering the entire plant body
• Protects plant from water loss, injury, infection
• In leaves, has small pores called stomata for
gas exchange
• Stomata have guard cells that open and close the pore
• In desert plants, epidermis is thick with waxy coating (cuticle)
to prevent water loss
• May have hair-like structures (trichomes)
• In older plants, outer layer of epidermis is replaced by cork
• Made of dead cells without intercellular spaces
• Cell walls are thick due to deposition of suberin (waxy
substance)
• Protects plant from mechanical injury, water loss, temperature
changes
• Does not allow gas exchange, so has lenticels (small pores)
• Example: Cork of bottle comes from bark of cork oak tree!
Stomata are like tiny doors on leaves! They open during day to let COâ‚‚ in for photosynthesis and let Oâ‚‚ out. They also help in releasing excess water (transpiration). At night, they close to prevent water loss. Smart, isn't it?
Animal tissues are classified into four main types based on their function: Epithelial Tissue, Connective Tissue, Muscular Tissue, and Nervous Tissue.
Epithelial tissue forms the protective covering of the body and lines internal organs and cavities.
Epithelial tissue is like the wallpaper or tiles in your house! It covers all surfaces - outer (skin) and inner (lining of stomach, intestines, blood vessels). It's the protective covering!
1. Simple Epithelium: Single layer of cells
• Squamous (flat): Found in blood vessels,
alveoli (air sacs in lungs). Allows easy diffusion.
• Cuboidal (cube-shaped): Found in kidney
tubules, glands. Provides mechanical support.
• Columnar (column-shaped): Found in intestine,
stomach lining. Helps in absorption and secretion.
• Ciliated (with hair-like cilia): Found in
respiratory tract. Cilia move to push out dust and mucus.
2. Stratified Epithelium: Multiple layers of
cells
• Found in skin, mouth, esophagus
• Provides protection against wear and tear
• Upper layers keep replacing as they wear out
3. Glandular Epithelium:
• Specialized for secretion
• Forms glands that secrete substances (sweat, saliva, hormones,
digestive juices)
When you get a small cut, your skin heals within days. This is because epithelial cells of skin divide rapidly to replace damaged cells. That's why epithelial tissue is great at repair!
Connective tissue connects, supports, and binds different tissues and organs in the body.
Connective tissue is like the packaging material, glue, and structural framework that holds everything together! It connects different parts, provides support, and fills spaces - like foam packaging protects items in a box.
1. Areolar Tissue:
• Found between skin and muscles, around blood vessels and
nerves
• Fills spaces, provides support
• Helps in tissue repair
2. Adipose Tissue:
• Stores fat below the skin and around organs
• Acts as insulator (keeps body warm)
• Acts as shock absorber
• Provides energy reserve
3. Dense Connective Tissue:
• Forms tendons (connect muscles to bones) and ligaments (connect
bones to bones)
• Very strong and has great tensile strength
4. Cartilage:
• Solid but flexible
• Found in nose, ear, joints between bones
• Provides support and reduces friction
• No blood vessels
5. Bone:
• Hardest connective tissue (due to calcium and phosphorus
salts)
• Forms skeleton
• Provides shape, support, protection
• Bone marrow produces blood cells
6. Blood:
• Liquid connective tissue
• Plasma (liquid matrix) contains blood cells
• Red Blood Cells (RBCs) carry oxygen
• White Blood Cells (WBCs) fight infections
• Platelets help in blood clotting
• Transports nutrients, hormones, waste
You might wonder - blood is liquid, how is it connective tissue? Blood connects all parts of body by transporting materials! It carries oxygen from lungs to cells, food from intestine to cells, and waste from cells to kidneys. It's the body's transport system!
Muscular tissue consists of elongated cells called muscle fibers that can contract and relax, producing movement.
Muscle cells are like rubber bands that can stretch and shrink! When they contract (shorten), they pull bones or organs, causing movement. Your every movement - walking, eating, even blinking - involves muscles!
1. Skeletal Muscle (Striated Muscle / Voluntary
Muscle):
• Attached to bones
• Long, cylindrical, multinucleated cells
• Have light and dark bands (striations) - look striped
• Under voluntary control (you can control them)
• Examples: Muscles of arms, legs, back
• Get tired quickly
2. Smooth Muscle (Unstriated Muscle / Involuntary
Muscle):
• Found in walls of internal organs
• Spindle-shaped, uninucleated cells
• No striations (smooth appearance)
• Not under voluntary control (work automatically)
• Examples: Muscles in stomach, intestine, blood vessels
• Don't tire easily
3. Cardiac Muscle (Heart Muscle):
• Found only in heart
• Cylindrical, branched, uninucleated cells
• Have faint striations
• Involuntary but rhythmic
• Never tire - work throughout life!
• Cells are interconnected for coordinated contraction
Voluntary muscles: You can control them. Try
moving your hand - you decide when to move it. These are skeletal
muscles.
Involuntary muscles: You cannot control them.
Your heart keeps beating, stomach keeps digesting food even when
you're sleeping! These are smooth and cardiac muscles.
Nervous tissue is specialized for receiving stimuli and conducting electrical impulses (messages) throughout the body.
Nervous tissue is like the internet or telephone network of your body! It receives information (you touch hot pan), processes it in brain, and sends response (pull hand back) - all in milliseconds! It's the body's communication system.
Neuron (Nerve Cell): The basic unit of nervous
tissue
Parts of a Neuron:
1. Cell Body: Contains nucleus and cytoplasm
2. Dendrites: Short, branched projections that
receive messages from other neurons
3. Axon: Long projection that carries messages
away from cell body to other neurons or muscles
4. Nerve Ending: Terminal branches of axon that
pass message to next neuron
The junction between two neurons is called a
synapse.
When you accidentally touch something hot:
1. Sensory neurons in skin detect heat (stimulus)
2. Message travels through neurons to spinal cord
3. Spinal cord immediately sends signal back
4. Motor neurons carry signal to muscles
5. Muscles contract and pull hand away
This happens so fast that you pull your hand before you even feel
pain! This quick automatic response is called reflex action.
| Feature | Plant Tissues | Animal Tissues |
|---|---|---|
| Growth | Localized (at specific points - meristems) | Throughout the body |
| Cell Wall | Present | Absent |
| Intercellular Spaces | Generally present | Generally absent (except loose connective tissue) |
| Dead Tissue | Many tissues are dead (sclerenchyma, xylem vessels) | Most tissues are living |
| Movement | No movement, so need more supportive tissues | Can move, have specialized tissues for movement |
| Feature | Skeletal | Smooth | Cardiac |
|---|---|---|---|
| Location | Attached to bones | Internal organs | Heart |
| Striations | Present | Absent | Faint |
| Control | Voluntary | Involuntary | Involuntary |
| Cell Shape | Long, cylindrical | Spindle-shaped | Cylindrical, branched |
| Nuclei | Many (multinucleated) | One (uninucleated) | One (uninucleated) |
| Fatigue | Tire quickly | Don't tire easily | Never tire |
Q1. Why do plants have more dead tissue compared
to animals?
Answer: Plants don't move, so they need more
supportive and protective tissues. Dead tissues like sclerenchyma
and xylem vessels provide this support. Animals move, so they need
living, flexible tissues.
Q2. Name the tissue present in the brain.
Answer: Nervous tissue (made of neurons).
Q3. Why are xylem and phloem called complex
tissues?
Answer: Because they are made up of more than one
type of cells working together.