Reproduction and Growth of Plants

Reproduction and Growth of Plants

Middle School

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Learning Objectives

• Describe a plant cell and how its main parts work together.

• Explain the differences between sexual and asexual reproduction in plants.

• Identify different methods of pollination and seed dispersal.

• Explain how environmental and genetic factors influence plant growth.

Key Vocabulary

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Cell Wall

A rigid layer that provides structure and support to plant cells, helping them keep their shape.

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Cell Membrane

This flexible barrier carefully controls all the substances that are entering and leaving the living cell.

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Chloroplast

This is the specific site of photosynthesis, the important process where plants make their own food.

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Mitochondria

Often called the 'powerhouse,' it is responsible for releasing usable energy from food for the cell.

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Nucleus

Considered the control center, the nucleus contains the cell's important genetic material that directs all activities.

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Asexual Reproduction

This type of reproduction is when a new plant grows from a part of the parent plant.

Key Vocabulary

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Sexual Reproduction

This type of reproduction involves male sperm and a female egg to create a new seed.

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Pollination

Pollination is the important process of transferring pollen from a male to a female plant structure.

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Tropism

Tropism is a plant's natural growth response that is directed toward or away from a stimulus.

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Gravitropism

This is a plant's specific growth response in relation to the pull of Earth's gravity.

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Phototropism

Phototropism describes how a plant grows or bends in response to a light source.

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The Plant Cell: A System

• All plants are made of cells, the basic building blocks of all life.

• Each cell has special structures called organelles that perform specific jobs for the cell.

• The cell membrane controls what can enter and leave the plant cell.

• The rigid cell wall is found outside the membrane and provides structural support.

Multiple Choice

What are the basic building blocks that make up all plants?

• Organelles

• Cells

• Cell walls

• Cell membranes

Multiple Choice

How do the primary functions of the cell wall and the cell membrane differ?

• The cell wall provides support, while the cell membrane controls what passes through.

• The cell wall holds the organelles, while the cell membrane provides energy.

• The cell wall allows entry and exit, while the cell membrane provides rigid structure.

• The cell wall is flexible, while the cell membrane is rigid.

Multiple Choice

What would be the most likely consequence for a plant cell if its cell wall were damaged?

• The cell would create too many new organelles.

• The cell would lose its rigid structure and support.

• The cell would not be able to control what enters or leaves.

• The cell would stop being a basic building block of life.

Energy and Control in Plant Cells

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Chloroplasts

• ​These organelles are responsible for photosynthesis in the plant cell.

• ​​They use sunlight to convert water and CO₂ into food.

• ​This process creates the sugary food that the plant needs.

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Mitochondria

• ​These are called the 'powerhouses' of the cell.

• ​​They break down sugars to release energy for all cell functions.

• ​This process of releasing energy is called cellular respiration.

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Nucleus

• ​The nucleus acts as the control center of the plant cell.

• ​​It contains the plant’s genetic material that directs its activities.

• ​This organelle directs growth, reproduction, and other cell functions.

Multiple Choice

Which part of the plant cell is considered the 'control center' and why?

• The nucleus, because it contains the genetic material that directs cell activities.

• The chloroplasts, because they use sunlight to create food for the cell.

• The mitochondria, because they are called the 'powerhouses' of the cell.

• The cell wall, because it provides a rigid structure for the plant.

Multiple Choice

What is the relationship between chloroplasts and mitochondria in a plant cell?

• Chloroplasts produce the sugar that mitochondria then break down to release energy.

• Mitochondria create energy from sunlight, which chloroplasts then store as sugar.

• Chloroplasts release energy from water, and mitochondria use it to make sugar.

• Mitochondria produce genetic material that chloroplasts use to create food.

Multiple Choice

If a plant cell's mitochondria were damaged, what would be the most likely immediate consequence?

• The cell would not be able to release energy from sugar to power its functions.

• The cell would be unable to convert sunlight into sugary food.

• The cell's genetic material would no longer be able to direct growth.

• The cell would create too much sugary food and not be able to store it.

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How Plants Reproduce

Asexual Reproduction

• ​A portion of a plant, like a stem or leaf, develops into a new plant.

• ​​The new plant is genetically identical to the parent, making it an exact copy.

• ​'Hens and chicks' plants reproduce this way when new 'chicks' grow from the main plant.

Sexual Reproduction

• ​This method involves a male reproductive cell (sperm) and a female reproductive cell (egg).

• ​​This process, called fertilization, results in a seed with mixed genetic material.

• ​The new plant that grows from the seed is genetically unique.

Multiple Choice

What is the main difference in the offspring created by asexual and sexual reproduction in plants?

• Asexually produced plants are genetically identical to the parent, while sexually produced plants are genetically unique.

• Asexually produced plants grow from seeds, while sexually produced plants grow from stems or leaves.

• Asexually produced plants are always much smaller than sexually produced plants.

• Asexually produced plants require fertilization, while sexually produced plants do not.

Multiple Choice

How does sexual reproduction result in a plant that is genetically unique?

• It combines genetic material from a male cell and a female cell during fertilization.

• It creates a new plant from a portion of the parent plant, like a stem or leaf.

• It produces a new plant that is an exact copy of the single parent plant.

• It relies on a single parent plant to create offspring without a seed.

Multiple Choice

A gardener sees that their 'hens and chicks' plant has several new, smaller plants growing from its base that look exactly like the parent. What conclusion is best supported by this evidence?

• The plant reproduced asexually, creating a genetically identical copy from a part of the parent.

• The plant must have reproduced sexually, because it created multiple new plants.

• The plant was pollinated by an insect, resulting in fertilization and new seeds.

• The plant's seeds were spread by the wind, leading to new plants growing nearby.

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Reproduction in Plants

• Seedless plants, like mosses and ferns, reproduce using tiny cells called spores.

• Seed plants undergo sexual reproduction, producing pollen grains and one or more eggs.

• In flowerless seed plants, a male cone produces pollen and a female cone holds eggs.

• In flowering plants, the pistil is the female organ and the stamen is the male organ.

• Dispersal of spores, seeds can happen with help of animals, birds, wind, water, etc.

Multiple Choice

What is the primary way that seedless plants, like mosses and ferns, create new plants?

• By releasing spores into the environment

• By developing seeds inside a flower

• By using pollen from male cones

• By growing from eggs in a pistil

Multiple Choice

What reproductive function do the stamen in a flowering plant and the male cone in a pine tree have in common?

• They both are involved in producing pollen for reproduction.

• They both contain the female eggs for reproduction.

• They both grow into new plants after being fertilized.

• They both rely on insects to be able to reproduce.

Multiple Choice

A strong gust of wind blows through a forest containing both pine trees and ferns. Based on their reproductive methods, what is the most likely outcome?

• The wind helps spread both the spores from the ferns and the pollen from the pine trees.

• The wind is necessary for the ferns to make spores but not for the pine trees.

• The wind helps the pine trees by spreading their seeds, but does not affect the ferns.

• The wind only helps flowering plants and would have no effect on either plant.

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Pollination and Seed Dispersal

• Since plants cannot move, pollinators like bees help transfer pollen between flowers.

• Wind dispersal carries light seeds, like dandelions with 'parachutes' and maples with 'propellers'.

• Water dispersal moves seeds that can float, such as coconuts and mangroves.

• Animals spread seeds by carrying them on fur or eating fruits like blackberries.

Multiple Choice

What is the primary reason plants rely on external factors like wind, water, and animals?

• Because they need protection from harsh weather.

• Because they cannot move to reproduce and spread their offspring.

• Because they require animals to find sunlight for them.

• Because their roots need help finding water in the soil.

Multiple Choice

What is the relationship between a seed's structure and how it is scattered?

• The physical characteristics of a seed determine its method of dispersal.

• The color of a seed determines how far it will travel.

• All seeds are dispersed by animals that eat fruit.

• Heavy seeds are most easily carried by the wind.

Multiple Choice

If bees were to disappear from an ecosystem, what would be the most likely consequence for the plants that rely on them?

• The plants would not be able to get enough sunlight.

• The production of fruits and seeds would decrease significantly.

• The plant's seeds would not be able to float on water.

• The plant's leaves would be eaten by other insects.

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What Affects Plant Growth?

Genetic Factors

• Plants inherit genes from their parents, which determine their specific traits and characteristics.

• These genetic instructions are stored in the nucleus of each one of the plant's cells.

• They control traits like flower color, leaf shape, and the final height of the plant.

Environmental Factors

• A plant’s surroundings, such as light and temperature, influence its overall development and health.

• The amount of moisture available, like in a drought, can significantly limit plant growth.

• The quality of the soil, including its salt levels, also plays a crucial role.

Multiple Choice

What are the two main types of factors that influence how a plant grows?

• Genetic and environmental factors

• The color of the flowers and the shape of the leaves

• The amount of light and the quality of the soil

• The plant's parents and its cells

Multiple Choice

How do a plant's genes influence its traits, such as flower color or final height?

• They provide instructions stored in the nucleus of each cell.

• They absorb sunlight and water from the environment.

• They change based on the temperature of the surroundings.

• They are only determined by the quality of the soil.

Multiple Choice

A plant has genes to grow very tall, but it is planted in poor soil and given very little light. What is the most likely outcome for the plant?

• Its growth will be limited by its environment.

• It will grow tall because of its genetic instructions.

• It will change its genes to adapt to the poor conditions.

• Its flower color will change, but its height will not be affected.

Plant Responses to Stimuli: Tropisms

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Phototropism

• This is a plant's growth response toward a light source.

• It helps plants get the most energy for making their food.

• The stem of the plant will bend toward the light.

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Thigmotropism

• This is a plant's growth or movement in response to touch.

• A vine wrapping its tendrils around a fence is an example.

• This response provides the plant with needed stability and support.

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Gravitropism

• This is a plant’s growth in response to the pull of gravity.

• Stems grow upward, which is away from the pull of gravity.

• Roots grow downward, into the soil, toward the pull of gravity.

Multiple Choice

Which statement best defines a tropism?

• A plant's growth response to an external stimulus

• The process of a plant making its own food

• The way a plant absorbs water from the soil

• The method a plant uses to reproduce

Multiple Choice

How do the functions of phototropism and thigmotropism differ?

• Phototropism helps a plant get energy, while thigmotropism provides a plant with support.

• Phototropism provides a plant with support, while thigmotropism helps a plant get energy.

• Phototropism helps a plant find water, while thigmotropism helps it avoid gravity.

• Phototropism helps a plant grow taller, while thigmotropism helps it change color.

Multiple Choice

If a potted plant is knocked over but continues to be watered, what will most likely happen to the stem and roots over time due to gravitropism?

• The stem will bend and grow upward, while the roots will bend and grow downward.

• The entire plant will stop growing until it is turned upright again.

• The roots will bend and grow upward, while the stem will bend and grow downward.

• Both the stem and the roots will continue growing straight in the direction they were pointing.

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Common Misconceptions

Misconception	Correction
The cell wall and cell membrane do the same job.	The cell wall gives structure; the membrane controls what enters and exits.
All plants reproduce using seeds.	Some plants, like ferns and mosses, reproduce using spores.
Plants do not react to their surroundings.	Plants respond to their environment through movements called tropisms.

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Summary

• Plant cells have a cell wall, nucleus, and chloroplasts for photosynthesis.

• Plants reproduce asexually to make identical copies or sexually for unique offspring.

• Pollination and seed dispersal by wind, water, or animals help plants reproduce.

• A plant's growth is determined by its genes and its environment.

Poll

On a scale of 1-4, how confident are you about the concepts of plant cells, reproduction, and growth?

• 1

• 2

• 3

• 4