CM

Modes of Reproduction (8.3) - Science 7 Unit 8: Reproduction and Genetics

Introduction

  • Nature creates life primarily through two modes of reproduction: sexual and asexual.
  • Sexual reproduction involves two parents and produces offspring that are a genetic mixture of both parents.
  • Asexual reproduction involves a single organism producing offspring that are genetically identical to the parent.
  • Both modes have distinct advantages and disadvantages that affect survival and adaptability in different environments.
  • Figure reference: Figure 1 shows a busy bee pollinating flowers as an example of sexual reproduction in nature.
  • Context example: In the Philippines, mango trees illustrate sexual reproduction through pollination and fruit development.

Learning Competency

  • Explain that genetic information is passed on to offspring from both parents by the process of meiosis and fertilization.
  • Understanding that meiosis and fertilization coordinate to transfer genetic information to offspring, producing genetic diversity in sexual reproduction.

Learning Targets

  • Understand sexual and asexual reproduction.
  • Differentiate reproduction methods based on the number of parents and similarities/differences of offspring.

Knowledge Kickstart (Multiple Choice Practice)

  • Question 1: What defines sexual reproduction?

    • A. There is involvement of only one parent.
    • B. The offspring is a clone of the parent.
    • C. There is fusion of genetic materials from two parents.
    • D. It is a rapid reproduction process.
    • Answer: C

  • Question 2: What is a key characteristic of asexual reproduction?

    • A. requires male and female gametes
    • B. produces genetically diverse offspring
    • C. involves only one parent
    • D. offspring undergo long development
    • Answer: C

  • Question 3: How does genetic diversity affect a species' survival in changing environments?

    • A. It has no significant effect.
    • B. It decreases survival chances.
    • C. It increases survival chances.
    • D. It speeds up the reproduction process.
    • Answer: C

  • Question 4: For species in stable environments, why might asexual reproduction be more suitable?

    • A. It increases genetic diversity.
    • B. It requires less time and resources.
    • C. It involves two parents.
    • D. It is better for long-term survival.
    • Answer: B

  • Question 5: In what way does sexual reproduction benefit plants like mango trees?

    • A. faster growth
    • B. identical offspring
    • C. increased genetic diversity
    • D. lower energy use
    • Answer: C

  • Question 6: How might asexual reproduction benefit organisms in an unchanging environment?

    • A. by creating genetic diversity
    • B. by allowing rapid population growth
    • C. by requiring two parents
    • D. by demanding more energy
    • Answer: B

  • Question 7: What is a disadvantage of sexual reproduction in terms of energy and resources?

    • A. It requires minimal energy.
    • B. It is less time-consuming.
    • C. It demands significant energy and resources.
    • D. It leads to rapid population growth.
    • Answer: C

  • Question 8: Analyzing the reproductive methods, which would be more vulnerable to widespread diseases?

    • A. sexually reproducing species
    • B. asexually reproducing species
    • C. both are equally vulnerable
    • D. neither is vulnerable
    • Answer: B

  • Question 9: In an unstable ecosystem, which reproduction strategy might offer better survival prospects?

    • A. rapid asexual reproduction
    • B. genetic diversity through sexual reproduction
    • C. equal use of both methods
    • D. avoiding reproduction
    • Answer: B

  • Question 10: What would be a major concern in using asexual reproduction for agricultural crops?

    • A. slow growth rate
    • B. high genetic diversity
    • C. vulnerability to disease
    • D. high energy costs
    • Answer: C

  • Warm-Up (Potato Activity) — Quick checks:

    • 1) Changes observed: sprouting, increase in size, color changes, indicating growth of a new plant from a bud.
    • 2) These changes occurred due to a bud (eye) that can grow into a new plant, illustrating asexual reproduction.
    • 3) This activity relates to asexual reproduction because a part of the parent plant forms a new, genetically identical plant.

Warm-Up Materials and Procedure (Summary)

  • Materials: potato, knife, glass of water, paper and pencil.
  • Procedure: cut a small piece of potato with a bud, place in water, observe daily for a week, sketch growth, note changes.
  • Observation Table (Table 1): track date, sketch, and observations.
  • Condition: place in a well-lit area, not direct sun.

Learn about It: Sexual Reproduction

  • Definition: Sexual reproduction involves the fusion of genetic material from two different parents through gametes (sex cells).
  • Gametes: mature haploid germ cells that unite with the opposite sex to form a zygote. In humans, sperm (male) and egg (female).
  • Example: In the Philippines, mango trees undergo pollination where pollen from the stamen (male part) fertilizes the pistil (female part). This leads to fruit development and offspring with mixed traits (genetic diversity).
    • Genetic diversity means individuals in a population have unique gene combinations, which helps populations withstand changing environments.
  • Key concept: Meiosis produces gametes with half the chromosome number; fertilization restores the full chromosome set.
  • Important term: A gamete is a mature haploid cell that fuses with another gamete to form a zygote.
  • Significance: Genetic diversity from sexual reproduction improves adaptability and disease resistance.
  • Visual cue: Figure 1 illustrates pollination as a sexual reproduction process.

Meiosis and Gamete Formation

  • Meiosis: a two-step division process that halved the chromosome number and shuffled chromosomes to create genetic diversity in gametes.
  • Gametes in humans: sperm (males) and eggs (females).
  • Chromosome numbers: somatic (body) cells are diploid (2n); gametes are haploid (n). Fertilization restores diploidy: 2n
    ightarrow n ext{ (gametes) }
    ightarrow 2n ext{ (zygote after fertilization)}.
  • Result: Offspring have a mix of parental traits due to recombination and independent assortment during meiosis.

Advantages and Disadvantages of Sexual Reproduction

  • Advantages:
    • Genetic diversity: enhances adaptation to environmental changes and resistance to diseases.
  • Disadvantages:
    • Finding a mate can be challenging; more time and energy required to produce and care for offspring.
    • Example: Philippine eagle’s long parental care period can exceed a year, which is energetically costly but improves offspring survival.
  • Did You Know?: The rafflesia, the world’s largest flower found in the Philippines, is a parasite that reproduces sexually.

Asexual Reproduction

  • Definition: Reproduction without the involvement of a mate; offspring are genetically identical to the parent.
  • When is it advantageous?
    • Efficient in stable environments where genetic adaptation is not urgently needed.
  • Common methods: budding, fragmentation, and regeneration.
  • Connection to potato warm-up: The potato experiment demonstrates how a single parent can produce identical offspring quickly.
  • Visual cue: Figure 2 shows plant cuttings reproducing asexually, producing identical new plants.
  • Key idea: Asexual reproduction can rapidly increase population size but lacks genetic diversity.

Advantages and Disadvantages of Asexual Reproduction

  • Advantages:
    • High efficiency and speed; no mating needed.
    • Useful in stable environments.
  • Disadvantages:
    • Lack of genetic diversity makes populations more vulnerable to diseases and environmental changes.
  • Example: A disease affecting one banana plant can spread rapidly among genetically identical plants.

Key Points (Summary)

  • Sexual reproduction combines genetic material from two parents, producing genetically unique offspring.
  • Asexual reproduction involves a single parent producing genetically identical offspring.
  • Genetic diversity from sexual reproduction aids adaptation and disease resistance.
  • Asexual reproduction is efficient in stable environments but lacks genetic diversity, increasing vulnerability to changes.
  • Each reproduction method has distinct advantages and disadvantages affecting survival and adaptability.

Check Your Understanding (True/Facts to Classify)

  • 1. Two parents are involved in the reproductive process, and the offspring is genetically unique. → Sexual
  • 2. A single potato plant can produce several new plants, all genetically identical to the original. → Asexual
  • 3. The Philippine eagle dedicates significant time and effort to nurturing its offspring, who inherit genetic characteristics from the mother and the father. → Sexual
  • 4. A disease affecting one banana plant in a plantation spreads quickly to other plants because they are genetically identical. → Asexual
  • 5. In humans, the merging of sperm and egg cells creates offspring with diverse genetic traits. → Sexual
  • 6. Starfish can regenerate lost arms, and these new arms are clones of the original. → Asexual
  • 7. Mango trees in the Philippines are pollinated, resulting in fruits that have genetic traits from both male and female parts of flowers. → Sexual
  • 8. An organism reproduces quickly without needing a mate and produces offspring that are exact genetic copies. → Asexual
  • 9. Genetic diversity is high, making organisms more adaptable to environmental changes and disease-resistant. → Sexual
    1. A stable environment is ideal for this type of reproduction because the offspring are genetically identical to the parent. → Asexual
    1. In a rapidly changing environment, this type of reproduction might be disadvantageous due to the lack of genetic diversity. → Asexual
    1. This reproduction method is less efficient in terms of the speed of producing new offspring. → Sexual
    1. It requires two parents and leads to genetically unique offspring, enhancing adaptability. → Sexual
    1. A single organism can reproduce rapidly, leading to a large number of offspring in a short period. → Asexual
    1. This type of reproduction is seen in the experiment with the potato, where a piece of potato can sprout and grow into a new plant. → Asexual

Self Assessment

  • I think I need more time and assistance.
  • I have a minimal understanding of it.
  • I am confident that I can do this with ease.
  • I can understand sexual and asexual reproduction.
  • I can differentiate based on number of parents and offspring similarities.

Reflection Prompts

  • I find the most interesting because ____.
  • I need to improve on __ because _.
  • I need to practice ___ because __.
  • I plan to _.

Attribution

  • Visual: Almond flowers closeup. Flowering branches of an almond tree in an orchard (licensed image).

References

  • Alberts, Bruce, et al. 2014. Molecular Biology of the Cell. 6th ed. New York: Garland Science.
  • Campbell, Neil A., and Jane B. Reece. 2011. Biology. 9th ed. Boston: Pearson.

Answer Key (Concise Reference)

  • Knowledge Kickstart (Answers)
    • 1. C
    • 2. C
    • 3. C
    • 4. B
    • 5. C
    • 6. B
    • 7. C
    • 8. B
    • 9. B
      1. C
  • Warm-Up Answers
    • 1. Changes include sprouting, size increase, color changes.
    • 2. Changes occurred due to a bud capable of growing into a new plant (asexual reproduction).
    • 3. Activity relates to asexual reproduction (identical offspring).
  • Check Your Understanding (Answers)
    • 1. Sexual
    • 2. Asexual
    • 3. Sexual
    • 4. Asexual
    • 5. Sexual
    • 6. Asexual
    • 7. Sexual
    • 8. Asexual
    • 9. Sexual
      1. Asexual
      1. Asexual
      1. Sexual
      1. Sexual
      1. Asexual
      1. Asexual

Notes on Formulas and Key Concepts (LaTeX)

  • Gamete chromosome number relationship:
    • Somatic cells are diploid: 2n
    • Gametes are haploid: n
    • Fertilization restores diploidy: n + n = 2n
  • Meiosis creates genetic diversity by recombination and independent assortment during cell divisions.

Figure References (from the module)

  • Figure 1: A busy bee pollinating flowers – highlights sexual reproduction in nature.
  • Figure 2: Through cutting, plants can reproduce asexually, creating new identical individuals.

Final Takeaway

  • Sexual reproduction increases genetic diversity and adaptability but requires more time and energy with two parents.
  • Asexual reproduction provides rapid population growth and efficiency but reduces genetic diversity, making populations more vulnerable to diseases and environmental changes.