Reproduction in Plants PDF

Chapter 14: Reproduction in Plants 1. Asexual and Sexual Reproduction ​ Reproduction is a characteristic of all living organisms. ​ Two main types: ○​ Asexual reproduction – involves only one parent, producing genetically identical offspring. ○​ Sexual reproduction –...

Chapter 14: Reproduction in Plants 1. Asexual and Sexual Reproduction ​ Reproduction is a characteristic of all living organisms. ​ Two main types: ○​ Asexual reproduction – involves only one parent, producing genetically identical offspring. ○​ Sexual reproduction – involves the fusion of gametes, producing genetically varied offspring. Key Terms: ​ Asexual reproduction: Offspring are genetically identical to the parent. ​ Sexual reproduction: Involves fusion of male and female gametes, leading to genetic variation. 2. Asexual Reproduction ​ Requires one parent; offspring are clones (genetically identical). ​ Example: Potato reproduction ○​ Tubers (e.g., potatoes) store nutrients and produce new plants from buds (eyes). ○​ New plants are identical to the parent plant. ​ Advantages: ○​ Fast reproduction ○​ No need for pollinators ○​ Efficient in stable environments ​ Disadvantages: ○​ No genetic variation ○​ Less adaptability to environmental changes 3. Sexual Reproduction ​ Requires two parents and produces genetically diverse offspring. ​ Gametes (sperm & egg) fuse in fertilization to form a zygote. ​ Example: Human reproduction  ○​ Human gametes have 23 chromosomes each, forming a zygote with 46 chromosomes. ​ Advantages: ○​ Genetic variation ○​ Better adaptability to changing environments ​ Disadvantages: ○​ Slower process ○​ Requires mate and specific conditions for fertilization Key Terms: ​ Gamete: A sex cell with half the chromosome number. ​ Fertilization: The fusion of gametes. ​ Zygote: A fertilized egg cell that develops into an organism. 4. Chromosomes and Cell Division ​ Organisms have two sets of chromosomes (diploid). ​ Gametes are haploid – contain half the usual chromosome number. ​ Mitosis: Produces genetically identical cells. ​ Meiosis: Produces gametes with half the chromosome number (haploid). Key Terms: ​ Diploid (2n): Cells with two complete sets of chromosomes. ​ Haploid (n): Cells with only one set of chromosomes. ​ Mitosis: Cell division for growth and repair. ​ Meiosis: Cell division producing gametes for reproduction. Summary: ​ Asexual reproduction is fast but lacks genetic diversity. ​ Sexual reproduction creates variation, increasing survival chances in changing environments. ​ Mitosis ensures growth & repair, while meiosis creates genetic diversity through gamete formation. Notes on Sexual Reproduction in Flowering Plants Flowers and Their Function  ​ Many flowering plants reproduce both sexually and asexually. ​ The main function of a flower is to produce gametes and ensure fertilization occurs. ​ Hermaphroditic flowers (e.g., Eucryphia) produce both male and female gametes. Structure of a Flower (Figure 14.6) ​ Sepals: Green, leaf-like structures that protect the bud before it opens. ​ Petals: Brightly colored to attract insects; some have guide-lines leading to nectar. ​ Nectary: Gland at the petal’s base, secretes sugary nectar to attract insects. Male Parts of a Flower (Stamens) ​ Stamens: The male reproductive organs. ○​ Filament: The stalk of the stamen. ○​ Anther: The pollen-producing structure at the top. ​ Pollen grains: ○​ Contain the male gametes. ○​ Have a hard coat for protection. ○​ Different species have different pollen shapes (smooth/spiky). Female Parts of a Flower (Carpel) ​ Carpel: The female reproductive organ. ○​ Ovary: Contains ovules (each holds a female gamete). ○​ Style: Connects the stigma to the ovary. ○​ Stigma: Sticky surface to catch pollen grains. Formation of Pollen Grains (Figure 14.8) 1.​ Young anther has four pollen sacs. 2.​ Pollen grains develop inside these sacs. 3.​ When the flower opens, the anther splits, releasing pollen. Pollination (Figure 14.11) ​ Definition: The transfer of pollen from an anther to a stigma. ​ Insect Pollination Process: ○​ Insects (e.g., honeybees) visit flowers for nectar. ○​ They brush against the anthers, picking up pollen. ○​ When visiting another flower of the same species, pollen sticks to the stigma, leading to pollination. ​ Self-pollination vs. Cross-pollination: ○​ Self-pollination: Pollen from the same flower lands on its own stigma. ○​ Cross-pollination: Pollen is transferred between different flowers of the same species (enhances genetic diversity). Fertilization ​ Happens inside the ovary when a pollen grain nucleus fuses with an ovule nucleus. ​ Leads to the formation of a zygote, which develops into a seed. Key Terms ​ Sepals: Protect the bud. ​ Petals: Attract pollinators. ​ Stamens: Male reproductive part. ​ Anther: Produces pollen. ​ Filament: Supports the anther. ​ Carpel: Female reproductive part. ​ Ovary: Contains ovules. ​ Ovules: Contain female gametes. ​ Style: Connects stigma to ovary. ​ Stigma: Catches pollen grains. ​ Pollination: Transfer of pollen to the stigma. Notes on Sexual Reproduction in Flowering Plants Investigating the Structure of a Flower (Activity 14.1) ​ Materials: A simple flower, transparent sticky tape (optional). ​ Procedure: 1.​ Observe and identify flower parts using Figure 14.5. 2.​ Remove and examine each part starting with sepals. 3.​ Create a table to document: ​ Name of flower part. ​ Stuck sample (if using sticky tape). ​ Function of the part. 4.​ Continue removing layers to the center (ovary and stamens). Reflection ​ Active learning (dissecting a flower) improves understanding better than looking at pictures. ​ Similar hands-on methods can be used for other topics. Wind Pollination ​ Some plants rely on wind to transfer pollen. ​ Example: Grass flowers (Figure 14.12). ​ Adaptations of wind-pollinated flowers: ○​ No petals → No need to attract insects. ○​ Large anthers → Dangle outside for wind exposure. ○​ Light pollen grains → Easily carried by the wind. ○​ Large, feathery stigmas → Increase pollen capture. ○​ Flexible filaments → Allow anthers to swing in the wind. ○​ Produce huge amounts of pollen → High wastage in dispersal. Comparison of Insect- vs. Wind-Pollinated Flowers (Table 14.1) Feature Insect-Pollinated Wind-Pollinated Petals Large, bright, with guide-lines Small, inconspicuous, or absent Scent Strongly scented No scent Nectary Present (produces nectar) Absent Anthers Inside flower (contact with insect) Dangle outside (exposed to wind) Stigma Inside flower (contacts insect) Large, feathery, dangles outside Pollen Grains Sticky/spiky to attach to insects Smooth, light for wind dispersal Pollen Quantity Moderate (some lost or eaten) Very large (most blown away) Self- vs. Cross-Pollination ​ Self-pollination: Pollen lands on the same flower’s stigma or another flower on the same plant. ​ Cross-pollination: Pollen is transferred to a different plant of the same species. ​ Importance: ○​ Cross-pollination increases genetic diversity. ○​ Self-pollination maintains genetic stability but reduces variation. Fertilization Process 1.​ After pollination, the male gamete (inside the pollen grain) reaches the stigma but has not yet fused with the female gamete. 2.​ Pollen tube formation: ○​ Pollen grain germinates and grows a tube down the style. ○​ Enzymes digest a path for the tube. 3.​ Pollen tube reaches the ovary and enters the micropyle of the ovule. 4.​ Male gamete (pollen nucleus) travels down the tube and fuses with the female gamete (ovule nucleus). 5.​ Fertilization is complete, forming a zygote. Seed Formation ​ After fertilization: ○​ Petals, sepals, and stamens wither and fall off. ○​ Ovules develop into seeds (each contains an embryo plant). ○​ Ovary develops into a fruit (protects the seeds). ​ Seeds enter a dormant state: ○​ Water is removed from the seed. ○​ Metabolic activity slows down. ○​ Dormancy allows seeds to survive harsh conditions (cold, drought). Key Terms ​ Self-pollination: Pollen transfers to the same flower or another on the same plant. ​ Cross-pollination: Pollen transfers to a flower on a different plant of the same species. ​ Pollination: Transfer of pollen grains from an anther to a stigma. ​ Pollen tube: The tube that grows from a pollen grain to the ovary, carrying the male gamete. ​ Micropyle: The small opening in the ovule where the pollen tube enters. ​ Fertilization: Fusion of the male nucleus (pollen) with the female nucleus (ovule). ​ Zygote: The first cell formed after fertilization, develops into an embryo plant. ​ Seed: A fertilized ovule that contains an embryo and can grow into a new plant. ​ Dormant: A state of inactivity where a seed’s metabolism slows down. Summary ​ Flowers facilitate sexual reproduction by producing gametes. ​ Insect-pollinated flowers are bright, scented, and have sticky pollen. ​ Wind-pollinated flowers have no petals, feathery stigmas, and produce light pollen. ​ Pollination can be self- or cross-pollination. ​ After pollination, fertilization occurs, forming seeds. ​ Seeds become dormant until conditions are favorable for germination. Investigating the Conditions Necessary for Seed Germination (Experimental Skills 14.1) Aim of the Experiment ​ To determine the necessary conditions for germination by providing different sets of seeds with different combinations of water, oxygen, temperature, and light. ​ To record and analyze the percentage of seeds that germinate under different conditions. Materials Needed ​ 50 small seeds (e.g., mustard or tomato seeds). ​ Five large test tubes.  ​ Cotton wool (wet and dry). ​ Water (boiled and unboiled). ​ Perforated zinc platform (to test oxygen availability). ​ Black paper (if a dark place is not available). Method 1.​ Set up five test tubes with the same number of seeds in each, as shown in Figure 14.17. 2.​ Place the test tubes in different environmental conditions to observe their effect on germination. 3.​ Observe the seeds daily, counting the number that have germinated. 4.​ Record the percentage of germinated seeds in a results table. 5.​ Use the data to determine the essential conditions for germination. Experimental Setup (Figure 14.17) Test Conditions Expected Outcome Tube A Wet cotton wool, warm, light place (control) Seeds should germinate normally. B Wet cotton wool, cold, dark place Germination will be slower or may not occur due to low temperature. C No oxygen, wet cotton wool, warm, light Little or no germination, as oxygen place (seeds placed on perforated zinc is essential for respiration. platform above water) D Boiled, cooled water (no oxygen), wet cotton No germination, as boiling removes wool, warm, light place dissolved oxygen needed for respiration. E Dry cotton wool, warm, light place No germination, as water is needed to activate enzymes and initiate growth. Conditions Required for Germination ​ Water:​ ○​ Softens the seed coat, allowing the embryo to grow. ○​ Activates enzymes to break down stored food. ○​ Supports transport of nutrients inside the seed. ​ Oxygen:​ ○​ Essential for aerobic respiration to produce energy (ATP). ○​ Required for growth and cell division. ​ Warmth:​ ○​ Ensures enzymes function efficiently, speeding up metabolic reactions. ○​ Seeds in cold conditions will show delayed or no germination. Question 1: Why Are These Conditions Necessary? ​ Water:​ ○​ Needed to rehydrate seed cells, enabling metabolic processes to start. ○​ Helps break down stored food to provide energy. ​ Oxygen:​ ○​ Used in cellular respiration, generating ATP for growth. ○​ Without oxygen, energy production stops, preventing germination. ​ Warmth:​ ○​ Enzymes that break down stored food work best at optimal temperatures. ○​ Cold temperatures slow down enzyme activity, preventing normal growth. Question 2: Why Do Some Seeds Require Light to Germinate?  ​ Example: Some rainforest tree seeds only germinate in the presence of light. ​ Reason: ○​ Ensures germination happens only when there is enough space for growth. ○​ If a large tree falls, more light reaches the forest floor, signaling a good time for germination. ○​ Prevents seeds from germinating in shade, where they may not survive. ○​ Helps the plant maximize survival chances by waiting for optimal conditions. Summary of Findings ​ Water, oxygen, and warmth are essential for germination. ​ Some seeds require light, especially those from rainforests, to ensure they grow in open spaces. ​ Seeds in dry, oxygen-deprived, or cold conditions fail to germinate. ​ Experiment results confirm these essential requirements for successful seed growth. These observations demonstrate how seeds are adapted to their environments and how different factors influence their germination success. Notes on Reproduction in Plants Self-Assessment of Results Table (Experimental Skills 14.1) When evaluating a results table for the seed germination experiment, consider: ​ Clarity of conditions: Does it clearly show what conditions were present in each test tube? ​ Accuracy of germination data: Does it correctly display the percentage of seeds that germinated? ​ Ease of interpretation: Can the best conditions for germination be identified quickly? Comparing Asexual and Sexual Reproduction Asexual Reproduction ​ Process: Parent cells divide by mitosis, producing offspring genetically identical to the parent (clones). ​ No genetic variation among offspring. ​ Common methods: ○​ Runners (e.g., strawberries). ○​ Bulbs (e.g., onions, tulips). ○​ Cuttings (e.g., roses in commercial farming). Sexual Reproduction ​ Process: Parent cells divide by meiosis to produce gametes, which have half the chromosomes. ​ Fertilization leads to new genetic combinations, increasing genetic variation among offspring. ​ Produces seeds in flowering plants, allowing offspring to be dispersed over a wide area. Advantages and Disadvantages of Asexual and Sexual Reproduction Feature Asexual Reproduction Sexual Reproduction Genetic variation None (offspring are clones) High (mixing of genes) Adaptability to Good if environment is stable Good if environment changes environment Speed of Fast (no need for pollination or Slower (requires gamete reproduction a mate) production and fertilization) Survival in isolation Can reproduce alone (e.g., a Needs a mate (or pollinators for single isolated plant) cross-pollination)  Resistance to Low (if a parent is susceptible, High (genetic diversity may disease all offspring are too) produce resistant individuals) Competition with High (offspring grow near Low (seeds disperse, reducing parent parent) competition) Examples of Asexual and Sexual Reproduction in Plants ​ Asexual reproduction:​ ○​ Tulips in each row are genetically identical (Figure 14.18). ○​ Commercial plant growers (e.g., roses) use asexual reproduction to create identical flowers. ​ Sexual reproduction:​ ○​ Used by farmers to create new plant varieties. ○​ Banana breeding programs now use sexual reproduction to introduce disease resistance. Self-Pollination vs. Cross-Pollination Self-Pollination ​ Process: A flower’s own pollen fertilizes its own stigma. ​ Example: Some violet flowers never open, allowing self-pollination (Figure 14.19). Advantages ✅ Ensures reproduction even without pollinators.​ ✅ Maintains stable, adapted genetic traits. Disadvantages ❌ Low genetic variation, which can be a disadvantage in changing environments. Cross-Pollination ​ Process: Pollen from one plant fertilizes the stigma of another plant of the same species. Advantages ✅ Increases genetic variation, improving adaptability.​ ✅ Higher chance of disease resistance. Disadvantages ❌ Requires pollinators or external factors (wind, insects).​ ❌ Risk of pollen not reaching another plant. Summary of Reproductive Strategies in Plants ​ Asexual reproduction is fast and efficient but lacks genetic variation. ​ Sexual reproduction introduces variation, which is beneficial in changing environments. ​ Self-pollination ensures reproduction in isolation, while cross-pollination enhances genetic diversity. ​ Both methods are useful, depending on environmental conditions and plant survival needs. 🌱🌷 These concepts are crucial in agriculture, conservation, and understanding plant evolution.