Big Idea: Characteristics from parents are passed to offspring in predictable ways

Transcription

1 Big Idea: Characteristics from parents are passed to offspring in predictable ways Unit 2 Lesson 3 Sexual and Asexual Reproduction Essential Question: How do organisms reproduce? Copyright Houghton Mifflin Harcourt Publishing Company

2 Unit 2 Lesson 3 Sexual and Asexual Reproduction One Becomes Two What is asexual reproduction? p114 Reproduction involves various kinds of cell division. Most single-celled organisms and some multicellular organisms reproduce asexually. In asexual reproduction, one organism produces one or more new organisms that are genetically identical to itself.

3 Unit 2 Lesson 3 Sexual and Asexual Reproduction P How do organisms reproduce asexually? The organism that produces the new organism or organisms is called a parent. Each new organism is called an offspring. The offspring produced by asexual reproduction are genetically identical to their parents. Prokaryotes, including bacteria, reproduce asexually by cell division. Some eukaryotes, including many multicellular organisms, reproduce asexually by more complex processes types of cell division called mitosis.

4 Unit 2 Lesson 3 Sexual and Asexual Reproduction P115 How do organisms reproduce asexually? Binary fission is the form of asexual reproduction in prokaryotes. Cell division Parent Cell splits into two Budding occurs when a bud grows on an organism and develops into a full-sized organism. Budding is the result of mitosis.

5 Unit 2 Lesson 3 Sexual and Asexual Reproduction How do organisms reproduce asexually? A spore is a specialized cell that can survive harsh conditions. Spores, produced asexually by one parent, are light and can be carried by the wind. Some plants can reproduce asexually by vegetative reproduction. Vegetative reproduction happens through mitosis. New plants grow from stems, roots, or leaves. Runners, tubers, plantlets Drop off plant and grow on their own P115

6 Unit 2 Lesson 3 Sexual and Asexual Reproduction Two Make One What is sexual reproduction? P116 Most multicellular organisms can reproduce sexually. In sexual reproduction, two parents each contribute a sex cell to the new organism. Half the genes in the offspring come from each parent. Males produce sex cells called sperm cells. Females produce sex cells called eggs. Sex cells are produced by meiosis. Sex cells have half of the set of genetic material found in body cells.

7 Unit 2 Lesson 3 Sexual and Asexual Reproduction P116 What is sexual reproduction? Sex cells have half of the set of genetic material found in body cells. A sperm and an egg join together in a process called fertilization. When an egg is fertilized by a sperm cell, a new cell, called a zygote, is formed. It has a full set of genetic material. The zygote develops into a new organism. It grows through mitosis.

8 Unit 2 Lesson 3 Sexual and Asexual Reproduction Odd Reproduction Multicellular organisms can reproduce asexually. P117 Some do this by parthenogenesis, in which the female produces young without fertilization. Other organisms reproduce asexually by regeneration. Other organisms reproduce asexually by fragmentation, in which segments fall off and become new organisms.

9 P Advantages Disadvantages Asexual Reproduction Sexual Reproduction

10 Unit 2 Lesson 3 Sexual and Asexual Reproduction P Added Advantage What are the advantages of each type of reproduction? Asexual reproduction has its advantages. It allows an organism to reproduce very quickly, and ensures that any favorable traits the parent has are passed on to the offspring. Reproduction can occur without a partner, and all offspring can reproduce. Copyright Houghton Mifflin Harcourt Publishing Company

11 Unit 2 Lesson 3 Sexual and Asexual Reproduction P What are the advantages of each type of reproduction? Sexual reproduction has its advantages. It increases genetic variation. Offspring have different traits, which improves the chance that at least some will survive. Some organisms can use both types of reproduction. This allows them to spread quickly, and adapt to changes in the environment as well. Copyright Houghton Mifflin Harcourt Publishing Company

12 P Advantages Disadvantages Asexual Reproduction Sexual Reproduction Quick Does not need a partner Offspring are identical All offspring are able to produce more offspring Can produce many offspring at one time Increases genetic variation offspring are not identical to parent Increases chance of survival in changing environments Requires complex structures Cannot adapt to a changing environment. No genetic variation (unless mutation occurs) Slow Does require partner (relationships)