Growth of Organisms

Growth of Organisms

Middle School

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Learning Objectives

• Describe how environmental factors like food, water, light, and space influence organism growth.

• Explain how plants respond to external stimuli through different types of tropisms.

• Define the role of genetic factors in determining the growth potential of an organism.

• Differentiate between environmental and genetic influences on growth.

Key Vocabulary

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Tropism

A plant's growth or movement in response to an external stimulus like light, water, or gravity.

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Phototropism

The growth of a plant in response to a light source to maximize its energy exposure.

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Gravitropism

A plant's growth response to the force of gravity, like roots growing down into the soil.

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Thigmotropism

The directional growth of a plant in response to touching a solid object, such as vines.

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Heredity

The passing on of genetic traits from parents to their offspring, influencing their potential for growth.

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Genes

Basic units of heredity passed from parent to child, determining potential traits like an organism's size.

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How the Environment Affects Growth

• An organism's growth depends on environmental factors like food, water, light, and space.

• A lack of water, or drought, can cause crops like corn to wither.

• Koi fish will grow much larger in a big pond than a small bowl.

• More CO₂ in the air helps poison ivy grow larger and more irritating.

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Multiple Choice

What primarily determines an organism's growth according to the principles of environmental science?

• The availability of resources like food, water, and space in the environment.

• The organism's ability to change its environment to suit its needs.

• The genetic makeup of the organism, which cannot be changed.

• The number of other organisms living in the same area.

Multiple Choice

Why would a koi fish likely grow much larger in a big pond than in a small bowl?

• The amount of space an organism has can limit its potential for growth.

• Koi fish in small bowls eat less food than koi fish in large ponds.

• Water temperature is the only factor that affects the growth of fish.

• Koi fish are a type of plant that withers without enough water.

Multiple Choice

Imagine two fields of corn. One field experiences a drought (a long period with no rain), while the other receives regular rainfall. What is the most likely prediction for the corn's growth?

• The corn in the field with regular rainfall will likely grow taller and healthier.

• The corn in the drought-stricken field will adapt and grow larger.

• Both fields of corn will grow to be the exact same size.

• The lack of water will make the corn plants produce more irritating oils.

Plant Responses to External Stimuli

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Phototropism

• ​Plants grow or move in a specific direction toward a light source.

• ​​This response helps plants get enough light for the process of photosynthesis.

• ​A houseplant on a windowsill bending toward the sun is an example.

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Gravitropism

• ​Plants change their growth in response to the force of gravity.

• ​​Roots display positive gravitropism by growing downward to find water and nutrients.

• ​The stem grows upward against gravity, showing negative gravitropism to get light.

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Thigmotropism

• ​This is a plant's growth response after it makes contact with something.

• ​​It is most common in climbing plants like vines that need support.

• ​Vines wrap around a trellis or another tree to help them climb.

Multiple Choice

Which statement best defines a plant's response to an external stimulus?

• The way a plant grows or moves in response to something in its environment.

• The process a plant uses to create its own food from sunlight.

• The way a plant produces seeds for reproduction.

• The process of a plant absorbing water through its roots.

Multiple Choice

What is the primary advantage for a plant's roots to grow downward and its stem to grow upward?

• To make the plant grow taller than other plants around it.

• To ensure the roots anchor the plant and absorb water, while the stem grows toward light for photosynthesis.

• To help the plant find a mate for reproduction.

• To protect the plant from being eaten by animals.

Multiple Choice

A climbing vine is planted in a pot placed against a solid wall. On the opposite side of the room, there is a bright window. What is the most likely way the vine will grow?

• The vine will grow straight up, ignoring both the wall and the window.

• The vine's roots will grow out of the pot toward the window.

• The vine's stem will bend toward the window, and its tendrils will try to attach to the wall for support.

• The vine will grow horizontally along the floor toward the dark wall.

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The Role of Genetics and Internal Stimuli

The Role of Genetics

• An organism's growth is fundamentally determined by its genes, which act as a blueprint.

• Gregor Mendel's work with pea plants established the core principles of heredity.

• For example, cattle need specific genes to grow to a large size for their breed.

Internal Stimuli

• Plants respond to internal signals, often using hormones to send messages throughout the organism.

• If a plant is short on water, hormones can signal for its roots to expand.

• This response helps the plant's root system find more water and essential nutrients.

Multiple Choice

What is the fundamental role of genes in an organism's growth?

• They act as a blueprint that determines how an organism develops.

• They directly absorb nutrients and water from the environment.

• They send messages throughout the organism in response to stimuli.

• They are created by an organism's response to its environment.

Multiple Choice

How do internal stimuli help a plant that is short on water?

• By signaling for a response that helps the plant find more water.

• By changing the plant's genes to better suit the environment.

• By stopping the plant's growth to conserve energy.

• By absorbing water directly from the air for the plant.

Multiple Choice

Cattle have genes that allow them to grow to a large size. How do both genetics and internal stimuli work together to control this process?

• The cattle's genes provide the blueprint for large growth, but hormones will signal for responses to environmental conditions.

• The cattle's genes will change throughout its life to adapt to the environment.

• The cattle will grow to a large size regardless of any internal stimuli.

• Hormones are the only factor that determines the final size of the cattle.

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Common Misconceptions

Misconception	Correction
An organism's growth is determined ONLY by its environment.	Genetics sets an organism's growth potential; the environment provides resources.
Plants are static and do not respond to their surroundings.	Plants respond to light, gravity, and touch through movements called tropisms.
All organisms of the same species grow to the same size.	Genetic differences cause size variations, even in the same environment.

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Summary

• Organism growth is influenced by environmental factors and genetic potential.

• Key environmental factors are food, water, light, and space.

• Plants respond to the environment through tropisms like phototropism and gravitropism.

• Genes determine an organism's maximum potential for growth and traits.

Poll

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