Atoms and Molecules

3.1 Why are Plant and Animal Tissues Different?

This section introduces the fundamental differences between plant and animal tissues, emphasizing their structural and functional adaptations. Plants are mostly fixed in one place and require support to stay upright. This is provided by the presence of a rigid cell wall in plant cells, which gives them strength and rigidity. In contrast, animal cells lack a cell wall, making them flexible and capable of changing shape, which facilitates movement and locomotion. Another key difference lies in nutrition: animals have tissues specialized for digestion of food obtained from various sources, while plants have tissues that enable photosynthesis, converting solar energy into food. Additionally, plants and animals have distinct tissues for transport—xylem and phloem in plants for water and food transport, and blood vessels in animals. Growth patterns also differ due to the variation in growth tissues. Understanding these differences helps explain how structure relates to function in multicellular organisms. **Table on page 3 (4×8)** | Experimental Jars | Length of onion root (cm) from the base of the bulb | | | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | | | Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 | | A | | | | | | | | | B | | | | | | | | **Table on page 8 (6×3)** | Function | Structure | Location in the body | | --- | --- | --- | | Exchange: Helps in rapid diffusion of liquids and gases | Single layer of thin, flat cells (Fig. 3.11a) | Lining of the tissue in the blood vessels and lungs | | Protection: Protects underlying tissues from mechanical injury, friction and entry of microbes | Many layers of cells; the outer cells are flat and tightly packed (Fig. 3.11b) | Skin, mouth and oesophagus | | Secretion: Production and secretion of mucus, enzymes, hormones, sweat saliva | Cells specialised for producing and releasing substances; may be cuboidal or columnar (Fig. 3.11c) | Salivary glands, sweat glands and stomach lining | | Sensory functions: Smell, taste, sound and balance | Specialised receptor cells having hair like cilia (Fig. 3.11d) | Nostrils, taste buds and inner ear | | Absorption: Efficient uptake of nutrients, water, etc. | Single layer of tall, pillar-like cells, often with hair-like structure (Fig. 3.11e) | Lining of small intestine | **Table on page 9 (4×3)** | Experiences | Observations | Questions | | --- | --- | --- | | When you get a small cut on your skin | Red blood oozes out from the cut. A clot is formed after some time. | What causes blood to clot? | | When you get a skin infection | The area turns red and perhaps slightly swollen. You may have a fever. | | | When you exercise or run | You breathe faster. Your face may turn red. | | **Table on page 10 (5×4)** | Action | Experience | Function | Identified connective tissue | | --- | --- | --- | --- | | Touch your elbow gently | A hard and rigid structure | Gives strength, support and protection | Bone (Fig. 3.12b) | | Press and fold your ear or gently press your nose and stop | A soft and flexible structure that retains shape again | Provides flexibility and cushions the ends of bones for shock absorption | Cartilage (Fig. 3.12c) | | Touch your forearm muscles and wiggle your fingers | Feel movement in the forearm even though fingers are far away | Connects muscle to bone, and thus, brings about movement | Tendon (Fig. 3.12c) | | Sit on a chair and move your leg upwards till your knee allows | The joint does not go beyond a limit | Connects bone to bone and provides stability, limits movement, and helps prevent dislocation | Ligament (Fig. 3.12c) | **Table on page 12 (8×5)** | Body parts | Complete rotation | Partial rotation | Bending | Turning, side-raising, up-down or any other movement | | --- | --- | --- | --- | --- | | Elbow | No | No | Yes | | | Shoulder | | | | | | Knee | | | | | | Neck | | | | | | Fingers | | | | | | Toes | | | | | | Wrist | | | | | **Table on page 15 (5×4)** | Conditions | | Composition of nutrient medium | Increase in fresh weight (mg) of the cells from initial weight | | --- | --- | --- | --- | | Light | Air | | | | ✓ | × | Solid medium + nutrients | reduced | | ✓ | ✓ | Liquid medium + nutrients | 20% increased | | × | ✓ | Liquid medium + nutrients | reduced | **Table on page 18 (7×4)** | S. No. | Age of the teak tree (Years) | DBH (Diameter at Breast Height) of tree (cm) | Number of annual rings formed | | --- | --- | --- | --- | | 1. | 5 | 4 | 5 | | 2. | 10 | 8 | 10 | | 3. | 20 | 24 | 20 | | 4. | 25 | 28 | 25 | | 5. | 30 | 32 | 30 | | 6. | 40 | 40 | 40 |

• Plant cells have rigid cell walls; animal cells do not.
• Plants are generally immobile and require support tissues; animals are mobile and have flexible cells.
• Plants synthesize their own food via photosynthesis; animals digest food.
• Transport tissues differ: xylem and phloem in plants; blood vessels in animals.
• Growth tissues vary, leading to different growth patterns in plants and animals.
• Tissue specialization reflects adaptation to organism lifestyle and environment.
• 📌 Cell wall: A rigid outer layer in plant cells providing strength.
• 📌 Photosynthesis: Process by which plants make food using sunlight.
• 📌 Xylem and Phloem: Conducting tissues in plants for water and food transport.

3.2 Tissues for Growth in Plants

Plants grow by increasing in length (height of stem and roots), girth (thickness of stem), and regrowing after damage such as grazing or cutting. This growth is possible due to the presence of meristematic tissues composed of actively dividing cells. These tissues are responsible for producing new cells that contribute to the plant's growth. Meristematic tissues are classified into three types based on their location and function: apical meristem, lateral meristem, and intercalary meristem. Apical meristems are located at the tips of roots and shoots and are responsible for lengthwise growth. Lateral meristems, found along the circumference of stems and roots, contribute to an increase in girth. Intercalary meristems, located at the base of internodes or above nodes, help plants grow after being cut or grazed, enabling regrowth. The cells of meristematic tissues are small, with thin walls, dense cytoplasm, and large nuclei, allowing continuous division. Some newly formed cells differentiate into permanent tissues specialized for functions like support, transport, or storage.

• Meristematic tissues consist of actively dividing cells enabling growth.
• Apical meristem causes increase in length at root and shoot tips.
• Lateral meristem causes increase in girth (thickness) of stems and roots.
• Intercalary meristem helps regrowth after cutting or grazing.
• Meristematic cells have thin walls, dense cytoplasm, and large nuclei.
• Differentiation converts meristematic cells into permanent specialized tissues.
• 📌 Meristematic tissue: Plant tissue with cells that divide actively.
• 📌 Apical meristem: Growth tissue at tips of roots and shoots.
• 📌 Lateral meristem: Growth tissue causing increase in girth.