4th Integrated Science: Sexual Reproduction in Plants (PDF)

1 SUBJECT: 4th Integrated Science TOPIC: SEXUAL REPRODUCTION IN FLOWERING PLANTS I. Sexual Reproduction in Plants: Sexual reproduction in plants involves the fusion of gametes, resulting in the formation of seeds and fruits. Let's explore the process and key components. Flowers:. ​ Flowers...

1 SUBJECT: 4th Integrated Science TOPIC: SEXUAL REPRODUCTION IN FLOWERING PLANTS I. Sexual Reproduction in Plants: Sexual reproduction in plants involves the fusion of gametes, resulting in the formation of seeds and fruits. Let's explore the process and key components. Flowers:. ​ Flowers are the reproductive structures of plants. ​ Parts of a flower include the petals, sepals, stamen, and pistil (carpel). ​ The petals attract pollinators, while the sepals protect the flower bud.  2 Pollination: : Pollination is the transfer of pollen grains from the anther to the stigma. Types of pollination include 1.​ self-pollination (pollen transfer within the same flower) and 2.​ cross-pollination (pollen transfer between different flowers). Advantages of cross-pollination include 1.​ increased genetic diversity and 2.​ the potential for better adaptation to changing environments. Agents of pollination include 1.​ wind, 2.​ Water, 3.​ insects, 4.​ birds, and other small animals like mice. 3  4. \Seed Formation 1.​ Zygote develops into an embryo – The zygote undergoes cell division and differentiation. 2.​ Ovule transforms into a seed – The outer layers of the ovule develop into the testa (seed coat). 3.​ Parts of the Seed: ○​ Embryo – The young plant inside the seed, consisting of: ​ Plumule – Develops into the shoot. ​ Radicle – Develops into the root. ○​ Cotyledons (Seed Leaves) – Store food for the young plant. ○​ Endosperm (in some seeds) – Additional food storage in seeds like maize and wheat. 4.​ Seed Dormancy: Some seeds remain inactive until conditions are right for germination.  5 III. Fruit Formation 1.​ Transformation of the Ovary: After fertilization: ○​ The ovary enlarges and develops into a fruit. ○​ The ovary wall thickens to form the pericarp, which protects the seeds. 2.​ Types of Fruits: ○​ True Fruits: Develop only from the ovary (e.g., mango, tomato). ○​ False Fruits: Develop from other parts of the flower (e.g., apple, cashew). 3.​ Functions of Fruits: ○​ Protect seeds from damage and drying out. ○​ Aid in seed dispersal. SEED STRUCTURE and GERMINATION Seeds have a protective outer layer called the seed coat or testa. The testa is formed from the outer layers of the ovule, and protects the seed.. Inside is the embryo which consists of one or more seed leaves or cotyledons. Also called the seed leaves, it is the large fleshy part of the inside of the seed and is the food source / store for the seed until the plant grows leaves. A young shoot (plumule), is the future stem of the plant body, its function is to give out leaves and make the plant capable of carrying out photosynthesis. The radicle; the young root. It is the first thing to emerge out of a seed and down into the ground to allow the seed to suck up water and nutrients.  6 Seed Dispersal Seeds must be spread away from the parent plant to reduce competition for light, water, and nutrients. 1.​ Methods of Seed Dispersal: ○​ Wind Dispersal: Lightweight seeds with wings or feathery structures (e.g., dandelion, maple). ○​ Water Dispersal: Seeds that float due to air pockets (e.g., coconut, water lily). ○​ Animal Dispersal: ​ Fleshy fruits eaten by animals, seeds excreted elsewhere (e.g., mango, cherry). ​ Sticky or hooked seeds attach to fur or feathers (e.g., burdock). ○​ Mechanical Dispersal: Fruits burst open, scattering seeds (e.g., peas, balsam). Germination of Seeds 1.​ Conditions Required for Germination: ○​ Water – Softens the testa and activates enzymes. ○​ Oxygen – Needed for respiration to provide energy.  7 ○​ Suitable Temperature – Activates enzymes for growth. 2.​ Stages of Germination: ○​ Water absorption (Imbibition): The seed absorbs water and swells. ○​ Enzyme activation: Stored food in cotyledons or endosperm is broken down for energy. ○​ Radicle emergence: The radicle grows downward to form roots. ○​ Plumule emergence: The plumule grows upwards to form the shoot. ○​ Seedling development: The young plant produces its own leaves and begins photosynthesis. Growth of a Bean Plant Instructions for Students: Graphing and Prediction Step 1: Plot the Graph 1.​ Draw axes on graph paper. ○​ X-axis (horizontal): Time (Weeks) → Label from 0 to 8. ○​ Y-axis (vertical): Height (cm) → Label from 0 to 50 cm. 2.​ Plot the given data points: ○​ (1, 2.5), (2, 6.0), (3, 12.0), (4, 20.5), (5, 29.0), (6, 38.0) 3.​ Join the points using a smooth curve or line of best fit. Step 2: Extrapolate Future Growth 1.​ Identify the trend in the graph (e.g., does the height increase steadily, slow down, or accelerate?). 2.​ Extend the line beyond the last recorded point (Week 6) to predict growth in Weeks 7 and 8. 3.​ Estimate the height for future weeks based on the curve: ○​ Week 7 ≈ 48 cm ○​ Week 8 ≈ 59 cm  8 Questions for Students to Answer 1.​ What pattern do you observe in the plant’s growth? 2.​ If the trend continues, what would be the estimated height at Week 10? 3.​ Suggest reasons why growth may slow down or stop after a certain time.  9 GROWTH PATTERNS IN PLANTS (A) Conditions Necessary for Germination of Seeds For a seed to germinate, three main conditions must be met: 1.​ Water (Moisture) ○​ Softens the testa (seed coat), allowing the embryo to expand. ○​ Activates enzymes that break down stored food into energy. ○​ Helps transport nutrients for growth. 2.​ Oxygen ○​ Required for aerobic respiration, which provides the energy needed for cell division and growth. ○​ Seeds buried too deep or in waterlogged soil may not get enough oxygen, leading to poor germination. 3.​ Suitable Temperature ○​ Influences enzyme activity, with different seeds requiring specific temperature ranges. ○​ Warm-season crops (e.g., maize) require higher temperatures (20–30°C), while cool-season crops (e.g., beans) germinate at lower temperatures (10–25°C). 💡 Without any of these conditions, germination may be delayed or fail completely. (B) Growth Patterns of Annual Plants (Bean and Corn) from Germination to Fruit Formation Annual plants complete their life cycle in one growing season, meaning they germinate, grow, flower, and produce seeds before dying. Beans (dicot) and corn (monocot) have distinct growth patterns. 1. Germination Stage ​ Bean (Dicot – Epigeal Germination) ○​ The cotyledons (seed leaves) are pushed above the soil as the hypocotyl (embryonic stem) elongates. ○​ The radicle (embryonic root) emerges first and grows downward. ○​ The plumule (embryonic shoot) emerges and develops leaves. ​ Corn (Monocot – Hypogeal Germination) ○​ The cotyledon (scutellum) remains below the soil, acting as a food source. ○​ The radicle emerges first, forming the primary root system. ○​ The coleoptile (protective sheath) pushes through the soil, covering the plumule until it reaches light.  10 2. Seedling Growth Stage ​ The cotyledons provide nutrients for initial growth, then wither as true leaves Bean: develop. ​ Corn: The coleoptile splits open, allowing the first leaves to emerge and begin photosynthesis. At this stage, both plants rely on nutrients, water, and photosynthesis to continue growing. 3. Vegetative Growth Stage (Leaf and Root Expansion) ​ Bean: ○​ The plant grows additional compound leaves. ○​ A taproot system develops, supporting water and nutrient absorption. ○​ Lateral branches may form. ​ Corn: ○​ A fibrous root system develops, spreading through the soil. ○​ More nodes and leaves emerge from the main stem. ○​ Growth is primarily vertical, unlike the branching seen in beans. 💡 This stage is crucial as plants begin producing food through photosynthesis to support further development. 4. Flowering Stage ​ Bean: ○​ Flowers develop from buds at leaf nodes. ○​ They are self-pollinated, meaning the plant can fertilize itself. ​ Corn: ○​ Produces separate male (tassel) and female (ear) flowers. ○​ Wind pollination transfers pollen from the tassel to the silks on the ears. 5. Fruit Formation and Maturation ​ Bean: ○​ Fertilized flowers develop into pods containing seeds. ○​ Pods mature, dry out, and split open to release seeds. ​ Corn: ○​ Each fertilized silk strand becomes a kernel. ○​ Kernels develop on the cob, filling with starch as they mature. ○​ The plant eventually dries out, signaling readiness for harvest. 11