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NCERT Class 9 Science Important Chapter 3 Tissues in Action
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Tissues in Action
Chapter – 3
| IMPORTANT QUESTION ANSWER |
Short Questions & Answers:
1. What is the hierarchy of organization in multicellular organisms?
Ans: In multicellular organisms, cells group together to form tissues, tissues form organs, organs form organ systems, and organ systems form the complete organism.
2. Define a tissue.
Ans: A tissue is a group of cells that are similar in structure and work together to perform a specific function.
3. What is the difference in how plants and animals obtain their nutrition?
Ans: Animals have tissues adapted to digest food from external sources, whereas plants have tissues that help them synthesize their own food using solar energy through photosynthesis.
4. Why do cells of meristematic tissues typically lack large vacuoles?
Ans: Meristematic cells lack vacuoles because they are tightly packed with dense cytoplasm and undergo continuous, rapid cell division.
5. What can scientists estimate by counting the annual growth rings of a tree?
Ans: Scientists can estimate the age of the tree and understand the climatic conditions under which it grew.
6. What is the process of differentiation in plants?
Ans: Differentiation is the process where cells from meristematic tissues lose their ability to divide and become specialized to perform specific functions, forming permanent tissues.
7. Which chemical deposition gives collenchyma cells their flexibility?
Ans: The deposition of pectin in the unevenly thickened corners of collenchyma cells provides them with flexibility.
8. Why are sclerenchyma cells hard and strong?
Ans: Sclerenchyma cells are hard and strong because their thick walls are heavily deposited with lignin.
9. What is the function of companion cells in the phloem?
Ans: Companion cells are specialized parenchyma cells that monitor and regulate the loading and unloading of sugars in the sieve tubes of the phloem.
10. What role does the cuticle play in plants?
Ans: The cuticle is a waxy layer of cutin covering the epidermis that reduces water loss, protects against mechanical injury, and prevents parasite invasion.
11. Which epithelial tissue is found in the lining of the small intestine and what is its function?
Ans: A single layer of tall, pillar-like cells forms the epithelium in the small intestine, which facilitates the efficient absorption of nutrients and water.
12. How does the matrix of bone differ from that of cartilage?
Ans: Bone has a hard, solid, and rigid matrix containing calcium and phosphorus compounds, while cartilage has a soft, flexible, and jelly-like matrix.
13. What is the structural difference between tendons and ligaments?
Ans: Tendons connect muscles to bones to bring about movement, whereas ligaments connect bones to bones to provide stability and limit excessive movement.
14. Where are smooth muscles found and what do they do?
Ans: Smooth muscles are found in organs like the stomach and intestines, where they help in slow, involuntary, and continuous movements like digestion.
15. What are the unique characteristics of cardiac muscle cells?
Ans: Cardiac muscle cells, found only in the heart, are cylindrical, branched, have a single nucleus, and feature faint striations.
16. What are the three primary parts of a neuron?
Ans: A neuron consists of a cell body (containing the nucleus), dendrites (which receive signals), and an axon (a long fiber carrying messages away to other cells).
17. What is the function of the skeletal system’s rib cage?
Ans: The rib cage acts as a protective framework for vital internal organs like the heart and lungs, and its flexibility allows it to expand and contract during breathing.
18. Which type of joint connects the skull to the backbone?
Ans: A pivot joint connects the skull to the backbone, allowing the head to move from side to side like a doorknob turning in its socket.
19. What is crown gall disease in plants?
Ans: Crown gall disease is caused by the bacterium Agrobacterium tumefaciens, which triggers rapid, uncontrolled cell division resulting in tumor-like swellings on plant stems.
20. What is totipotency?
Ans: Totipotency is the ability of certain mature, specialized cells to dedifferentiate, divide, and redifferentiate into a completely new organism under specific conditions.
Fill in the Blanks:
1. A __________ is a group of similar cells performing a specific function.
Ans: Tissue.
2. Meristematic tissues are responsible for __________ in plants.
Ans: Growth.
3. Sclerenchyma cells are hard due to the deposition of __________.
Ans: Lignin.
4. __________ tissue transports water and minerals from the roots to the rest of the plant.
Ans: Xylem.
5. A __________ joint connects the skull to the backbone.
Ans: Pivot.
True or False:
1. Plants make their own food through photosynthesis.
Ans: True.
2. Companion cells help in the loading and unloading of sugars in the phloem.
Ans: True.
3. Tendons connect bones to bones.
Ans: False.
4. Cardiac muscles are found only in the heart.
Ans: True.
5. Fixed joints allow free movement of bones.
Ans: False.
Long Questions & Answers:
1. Describe the major differences between plant and animal tissues based on their structure, function, and growth patterns.
Ans: Plant and animal tissues differ significantly due to their distinct lifestyles and functional needs:
(i) Structure and Mobility: Most plants are stationary and need structural support to stay upright, so their cells have a rigid cell wall that provides strength. In contrast, animals move around for food and shelter, so their cells lack a rigid cell wall; this cellular flexibility makes their bodies suitable for locomotion.
(ii) Nutrition: Animals have specialized tissues to digest externally obtained food, while plants possess tissues that utilize solar energy to synthesize food through photosynthesis. Both have distinct systems for transporting food and water.
(iii) Growth Patterns: The pattern of growth varies greatly. Plant growth is localized to specific regions where actively dividing cells (meristematic tissues) are present, allowing them to grow throughout their lives. Animals do not have these localized growth zones, and their growth is more uniform across the body.
2. What are meristematic tissues? Explain their three different types and their specific roles in the growth of a plant.
Ans: Meristematic tissues are groups of actively dividing cells in plants that are responsible for growth in different dimensions. The cells of these tissues are tightly packed, lack vacuoles, have thin cell walls, dense cytoplasm, and a prominent nucleus to support continuous rapid division.
The three main types are:
(i) Apical Meristem: Located at the growing tips of roots and shoots, this tissue is responsible for increasing the plant’s length (height of the stem and depth of the roots).
(ii) Lateral Meristem: Found arranged in a concentric ring in the stems of dicot plants, this tissue produces new cells inside and outside along the circumference, leading to an increase in the plant’s girth or diameter.
(iii) Intercalary Meristem: Situated at the base of internodes or just above the nodes, this tissue helps generate new branches or leaves, and allows plants like grasses to regenerate after being cut or grazed.
3. Explain the complex permanent tissues in plants, detailing the components and functions of both xylem and phloem.
Ans: Complex permanent tissues are composed of more than one type of cell that work together as a unit to perform conducting functions in plants.
There are two primary types:
(i) Xylem: This tissue transports water and dissolved minerals upwards from the roots to the rest of the plant and provides structural strength. It mostly consists of dead, thick-walled cells. Its components include tracheids and vessels (which are tubular and conduct water), xylem fibres (which provide strength), and xylem parenchyma (the only living component that stores food).
(ii) Phloem: This tissue transports synthesized food (sugars) from the leaves to other parts of the plant. Unlike xylem, phloem is primarily made of living cells. It consists of sieve tubes (tubular cells with perforated walls for transport), companion cells (which regulate the loading and unloading of sugars in the sieve tubes), phloem parenchyma, and phloem fibres (which provide structural support).
4. Describe the different types of muscular tissues found in the human body, focusing on their distinct structures and functions.
Ans: Muscular tissues in animals are responsible for bringing about movement and are classified into three types based on structure and control:
(i) Skeletal Muscles: These are attached to the skeleton and are responsible for voluntary movements that we consciously control, like walking or lifting. Structurally, they are made of long, cylindrical, unbranched, and multinucleate cells that exhibit light and dark bands (striations).
(ii) Smooth Muscles: These muscles handle involuntary movements that occur automatically, such as the passage of food through the stomach and intestines. Their cells are spindle-shaped, possess a single central nucleus, and lack any striations, enabling slow and continuous movements.
(iii) Cardiac Muscles: Found exclusively in the heart, these muscles tirelessly perform the involuntary rhythmic beating of the heart throughout life. Cardiac muscle cells are cylindrical, branched, and have a single nucleus with faint striations.
5. What is a joint? Detail the four major types of joints in the human musculoskeletal system and the specific movements they allow.
Ans: A joint is a junction where two or more bones meet, allowing the skeleton to move in coordination with muscles.
The four primary types of joints are:
(i) Ball and Socket Joint: Found in the shoulder, this joint features the rounded end of one bone fitting into the shallow hollow of another. It provides a wide range of motion, allowing forward, backward, sideways, and circular movements.
(ii) Hinge Joint: Located in the elbow and the knee, this joint operates like a door hinge, restricting movement strictly to one direction (bending and straightening).
(iii) Pivot Joint: This joint connects the skull to the backbone (vertebral column), allowing the head to smoothly rotate from side to side, much like a doorknob turning in its socket.
(iv) Fixed Joints: These joints tightly connect the flat bones of the skull. They are completely immovable, creating a solid and protective hard case to keep the brain safe during physical activity.
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