"Chapter 4: Animal Growth and Heredity"
Chapter 4: Animal Growth and Heredity Lesson 1: How Does Cell Division Affect Growth? Lesson 2: How are Characteristics Inherited? Lesson 3: What Other Factors Affect Characteristics? Lesson One: VOCABULARY: Life Cycle: The stages that a living thing passes through as it grows and changes. Mitosis: The process by which most cells divide. Chromosome: A threadlike structure in the nucleus, made up of DNA. Lesson One: How Does Cell Division Affect Growth? Growth and Development All living things begin life as a single cell. In plants and animals, the cells start dividing. The fully formed plant or animals is made up of trillions of cells. Even in adult organisms, cells continue to divide and replace the worn out cells. The new cells have the same function as the old cells. Lesson One: How Does Cell Division Affect Growth? Growth and Development As living things grow, they must pass through several stages which make up the life cycle. Some animals change a great deal as they grow into adults. Butterflies and other insects have one kind of body while young and another type of body when they become an adult. The stages they go through as they grow are called metamorphosis. Other animals do not change as much during their life cycle and look pretty much the same when they are young as when they are old except bigger. Lesson One: How Does Cell Division Affect Growth? CELL DIVISION The process by which most cells divide is called mitosis. Mitosis is controlled by the cells nucleus. The nucleus contains threadlike structures called chromosomes. Chromosomes are made up of chemical DNA. DNA has the information needed to direct a cells function and tell the cell when to divide. Lesson One: How Does Cell Division Affect Growth? In mitosis, each new cell gets a copy of the parent’s chromosomes. This passes along the DNA which is why the cells look and function just like the parent cells. New cells replace damaged tissue which is called regeneration. In humans, regeneration happens mostly for healing wounds. However, some animals can regenerate an entire body part (like a starfish). Lesson One: How Does Cell Division Affect Growth? Sexual and Asexual Reproduction: Sexual reproduction happens when two cells from two different individuals join and form a zygote. Organisms that reproduce sexually have 2 types of cells: Body cells and reproductive cells (or gametes). Gametes contain only half the number of chromosomes (23 chromosomes) as body cells. Once two gametes join, they have the same number of chromosomes as a body cell (46 chromosomes) has. Lesson One: How Does Cell Division Affect Growth? Some organisms have only one cell. When the cell divides, the whole organism reproduces. In asexual reproduction there is no joining of cells from different parents. Lesson Two: How Are Characteristics Inherited? VOCABULARY Inherited trait: A characteristic passed from parents to their offspring. Recessive trait: A trait that appears only if an organism has two factors, or genes, for that trait. Dominant trait: A trait that appears even if an organism has only one factor, or gene, for that trait. Gene: Part of the chromosome. It contains the DNA code for an inherited trait. Lesson Two: How Are Characteristics Inherited? How Characteristics are Inherited Inherited traits are characteristics passed from parents to their offspring. The way traits are passed from parents to offspring interested Gregor Mendel who studied this. Mendel found that a trait is controlled by a pair of factors (one from each parent). Mendel also learned that factors can skip a generation. Inheritance in all organisms (including people) works this way. Lesson Two: How Are Characteristics Inherited? Dominant and Recessive Traits Mendel did hundreds of crosses of pea plants and found that first generation plants were always tall. Mendel believed the first generation plants had a hidden factor for shortness. In pea plants, tallness is a strong or dominant trait. Even if an organism has only one factor for a dominant trait, that trait will appear. Shortness in a plant is a weak or recessive trait. A recessive trait appears only if an organism has two factors for that trait. If both a dominant factor and recessive factor are present, the dominant trait always appears. Lesson Two: How Are Characteristics Inherited? Adaptations Arctic foxes live in very cold places. An arctic fox has adaptations that keep it warm in the winter. Adaptations helps a living organism meet their basic needs in order to survive, find a mate, find shelter, hunt or hide. Adaptations are passed from parent to offspring and are inherited traits. Lesson Two: How Are Characteristics Inherited? Adaptations The second kind of adaptation is behavioral. There are 3 types Example: Snakes only move around before sunset or after of adaptations: sundown. During the hottest part of the day they will hide under a The first kind is physical. rock to stay cool. Example: An arctic fox has white fur in winter which helps it hide and more easily sneak up on prey. The third kind of adaptation is a life process. Example: A human’s body produces sweat. This helps keep the body from getting too hot. Lesson Two: How Are Characteristics Inherited? Survival and Reproduction: All animals have adaptations for survival. For example: porcupines have an adaptation that protects them from predators. Adaptations help animals survive so that they can reproduce. If a species cannot successfully reproduce, it may become extinct. Extinction is the death of all organisms of a species. Lesson Two: How Are Characteristics Inherited? Genes: Today, Mendel’s “factors” are called “genes”. A gene is part of a chromosome. Genes contain the DNA code (information) for inherited traits. Lesson Three: Other Factors that Affect Characteristics VOCABULARY: Instinct: is a behavior (way of acting) that an organism inherits. Learned behavior: a behavior that an animal acquires through experience. Environment: all of the things in an organism’s surroundings that affect it. Lesson Three: Other Factors that Affect Characteristics Instincts: A bird making a nest and a cat grooming itself are examples of instincts. An instinct is a natural behavior. Most instincts help an animal survive in its surroundings. Since instincts are inherited, they are passed from parents to offspring. Instincts are not just behaviors of one animal. Instincts are shared by all members of a species. Lesson Three: Other Factors that Affect Characteristics Learned Behaviors: Most cats are born with an instinct to hunt. But they need to learn hunting skills from adult cats. Knowing how to hunt is a learned behavior. A learned behavior is a behavior that an animal obtains by doing something. Not all learned behaviors are for survival. (tricks) Some animals can learn behaviors that are helpful to people. Lesson Three: Other Factors that Affect Characteristics Environmental Influences: Some behaviors are neither instinctual or learned. They are a result of environmental influences. An organism’s environment is everything in its surroundings that affect it. This may include water, food, air, landforms, and other living things. When an environment changes, all things that live there are affected. Often times animals must move in order to survive. Human activities can sometimes change an environment. Sometimes the environment causes a physical change in living things (pollution or poison can damage the DNA of living things.)