CHAPTER 13 - - - PLANTS



UNIT 15: Plant Notes

I. What is a Plant?

- Plants come in different shapes and sizes, but all plants share certain characteristics.

- Since plants are living, they all have the six basics characteristics of life: Have cells, Have

DNA or genetic material, Use Energy, Grow and develop, Reproduce & Respond to a stimulus

A. Plant Characteristics

1. Plants Make Their Own Food

- Plants need food, just like animals – but most plants do not get their food from other organisms. Instead, they make their own food through photosynthesis.

- Autotroph: An organism capable of making its own nutrients from inorganic sources through photosynthesis – involving light energy.

- Photosynthesis: The process by which some organisms use sunlight, carbon dioxide, and water to produce sugar and oxygen. (plants are producers)

∙ They get the energy for photosynthesis from sunlight (radiant energy).

- Almost all plants are green.

∙ Plants are green because they contain chlorophyll.

∙ Chlorophyll: is a green pigment that captures the energy of sunlight.

∙ Chlorophyll is found in organelles called chloroplasts. Chloroplasts

are mainly found in leaves, but can be found in other parts. Plants make their food in these chloroplasts.

2. Plants Have a Cuticle

- Most plants live on land, so why don’t they dry out? Plants are protected by a cuticle.

∙ Cuticle: A waxy layer that coats the surface of plants.

∙ The cuticle keeps moisture inside the plant. Why would desert plants tend to have thicker cuticles that plants living in wetter areas?

3. Plants Cells Have Cell Walls

- Plant cells are surrounded by a flexible cell membrane and a rigid cell wall.

- Cell Wall: A rigid layer surrounding the plant cell membrane made of a protein called cellulose that helps support and protect the cell.

- Cellulose: A type of carbohydrate.

- ONLY plants have cell walls and cell membranes.

B. The Origin of Plants

- The first plants appeared on Earth about 430 million years ago.

- Plants are in the Kingdom Plantae, but can be separated into different phylums.

- Plants have a lot in common with modern green algae. Both have the same kind of chlorophyll and have similar cell walls. Both store their energy in the form of starch and both have a two-part life cycle. Because of this, scientists think that plants and green algae share a common ancestor.

- The oldest known plant fossil is Cooksonia.

C. Types of Plants.

- Plant can be divided into two groups: Vascular Plants and Nonvascular Plants.

- Vascular Plants: A plant that has water-conducting tissues xylem and phloem.

∙ Seed Plants

- Flowering Plants (Angiosperms)

- Nonflowering Plants (Gymnosperms)

∙ Seedless Plants (Ferns, Horsetails, & Club Mosses)

- Nonvascular Plants: A plant that lacks the water-conducting tissues xylem and phloem. (Mosses, Liverworts, and Hornworts)

D. Nonvascular Plants

- There are 3 types of nonvascular plants – mosses, liverworts, and hornworts.

- These plants do not have true vascular tissues, although some mosses have simple water-conducting tissues.

- Nonvascular plants have a limited ability to move water or nutrients inside them. They must absorb water directly from their environment or from a neighboring cell. For this reason, mosses, liverworts, and hornworts are small and live in wet places.

∙ Mosses typically live together in large groups. They cover soil or rocks with a mat of tiny preen plants.

- Nonvascular plants also don’t have true roots, stems, or leaves.

∙ Rhizoids: Slender structures on moss plants that help hold the plant in place.

∙ Instead of stem and leaves, each moss plant has a leafy stalk.

- Sphagnum moss, a primary component of peat bogs, was used during World War I as an absorbent dressing for wounds. Its hollow cells enable it to absorb up to 20% of its own weight in water. In earlier times, it was also used for diapers, lamp wicks, and bedding. Today, gardeners use sphagnum moss to protect fragile plants during shipment.

E. Vascular Plants

- Vascular plants have tube-like structures for the internal transport of food and water through the plant = that’s why they are called vascular plant. All vascular plants have roots, stems and leaves.

- Vascular tissue can bring water from the ground to the leaves on top of the tallest trees.

- Because of this system, vascular plants can live in dryer climates and grow much bigger than nonvascular plants.

- Vascular Plants: A plant that has water-conducting tissues xylem and phloem

∙ Vascular tissue in plants are the “pipes” that transports nutrients for the plant.

∙ Xylem: Specialized plant tissue that transports water and minerals from one part of the plant to another. (roots to leaves)

∙ Phloem: Specialized plant tissue that transports nutrients and minerals from

one part of the plant to another. (leaves to roots)

- Food (glucose) made in the leaves is carried to where it is needed

in the tissue phloem.

F. Vascular Plants Without Seeds

- Seedless vascular plants include: Ferns, Horsetails, and Club Mosses.

- Ferns:

∙ Grow in many places (cold artic to the warm, tropical forests)

∙ Although most ferns are small plants, some tree ferns in the Tropics grow tall.

∙ Ferns are the most common group of seedless vascular plants

- Horsetails:

∙ There are only about 15 species alive today. (they were more common long ago)

∙ They are small and grow in wet, marshy places.

∙ Their stems are hollow and contain silica – the silica makes them feel gritty. (Early pioneers used them as “scouring rushes” to scrub pots and pans)

- Club Mosses:

∙ Grow in woodlands – but are not very common any more.

∙ Club mosses are not actually mosses but are another kind of seedless vascular plant like ferns & horsetails. Club mosses do have some vascular tissue.

G. Vascular Plants with Seeds but Without Flowers

- Gymnosperms: A type of vascular plant that produces seeds but not flowers or fruit.

∙ AKA: Evergreens: green all year; thin, needlelike leaves; pine cones.

- Types of Gymnosperms (Fig 9 – p. 324)

1. Conifers: Pine trees and their relatives. Conifers are the most common type

of gymnosperms. Conifers are commonly called evergreens.

- The oldest living trees are in this group = Bristlecone Pine.

2. Cycads: Were common millions of years ago. (about 140 species survive)

3. Ginkgoes: There is only one living species of ginkgo, the Ginkgo Tree.

4. Gnetophytes: Shrubs that grow in dry areas. (about 70 living species)

- All gymnosperms have seeds, which protect and nourish plant embryos.

H. Vascular Plants with Seeds and Flowers

1. Angiosperms: A type of vascular plant that produces seeds in flowers.

- There are about 235,000 species of angiosperms, more species than all other plant species combined.

- They can be found almost everywhere on land and come in many shapes & sizes.

- Examples: Dandelions, Waterlilies, Cactuses, Oaks, Tulips, Roses, & Grasses.

- Angiosperms produce flowers and fruits.

2. What Are Flowers For?

- Flowers help angiosperms reproduce. They help attract animals that carry pollen to other flowers.

∙ Pollinators: insects, birds, bats, other animals

- Pollen: The grains that surround and protect a plant’s sperm.

- Pollination: When pollen fertilizes a flower’s eggs.

3. What Are Fruits For?

- Fruits surround and protect seeds. Fruits help seeds survive as the seeds are moved to places where new plants can grow.

- Animals eat the fruits and discard the seeds – grow new plants.

- Seeds can travel by wind, animal, and water.

II. Structure and Function of Vascular Plants

- All vascular plants have certain structures in common. They all have vascular tissue, roots, stems, and leaves. Some also have seeds and some seed plants produce flowers and fruits.

- The 6 basic structures of plants are: Roots, Stems, Leaves, Seeds, Flowers & Fruits

- Hormones in plants create chemical signals (internal stimuli) that regulate many internal functions of plants: root growth, fruit production, & promote seed and bud germination.

A. Roots

1. Plant roots have 3 functions: (1) The roots supply plants with water and minerals absorbed from the soil. (2) Roots support and anchor plants. (3) Some roots store extra food made during photosynthesis – like a carrot.

2. Root Structure.

- Epidermis: The outer surface of roots.

- Root Hairs: Tiny hairs on the main roots that increase the surface area of the root so it can absorb more water and nutrients.

- Root Cap: a group of cells that protects the tip of a root and produces a slimy substance that makes it easier for the root to grow through soil.

∙ Roots grow from the tip.

3. Larger root systems are better adapted to dryer climates because an increase in root surface area increases the amount of water it can absorb at any particular time. Why would that be important?

4. Roots absorb nutrients from the soil. Nutrients get in the soil when living organisms (both plants and animals) die and their nutrients return to the ground (topsoil) through decomposition.

B. Stems

1. Stems vary greatly in shape and size. Most are above ground, but many plants have

underground stems as well.

3. Stems contain vascular tissue (phloem and xylem) that transport food, water, and nutrients.

4. Stem Functions (stems connect a plant’s roots to its leaves.)

- Stems support the plant body

- Stems also hold flowers up and display them to insects and other animals.

- Vascular tissue inside stems transports materials between the roots and the leaves.

- Some stems also store food and water. The white potato is an underground stem adapted to store starch, it is not a root.

5. Stem Types: Plant stems often determine the plant form, there are 6 main forms.

- Herbaceous: Stems that are soft, thin, and flexible. They are green and fleshy.

∙ Many plants with herbaceous stems only live 1 or 2 years.

∙ Herbaceous stems are soft, thin, and flexible which allows these plants to easily grow towards a light source. How might that be a beneficial adaptation?

∙ 4 Main Forms: Vines, Forbs, Grasses & Aquatic Plants

- Woody: Stems that are rigid and have bark and wood.

∙ They may live for several years.

∙ 2 Main Forms: Trees & Shrubs

C. Leaves

1. Leaves vary greatly in size and shape. They may be round, narrow, heart shaped, fan shaped, or needle shaped.

- Broad leaves are better adapted for wetter climates and areas of low light (such as the bottom of a forest). Why might that be?

- Small leaves, needles, and spines are better adapted to dryer climates to help prevent water loss through its stomata.

- The largest plant leaves in the world are those of the raffia plant of the Mascarene Islands, in the Indian Ocean, and those of the bamboo palm of South America

and Africa. These leaves can grow to nearly 20m in length.

- Some leaves have functions other than photosynthesis.

∙ Cactus leaves are modified to be pointy spines. The spines help protect the cactus from being eaten and also reduce water loss through stomata.

2. Leaf Function

- The main function of leaves it to make food (glucose) for the plant.

- Leaves capture the energy in sunlight and absorb carbon dioxide from the air.

3. Leaf Structure

- The structure of leaves is related to their main function – Photosynthesis.

- The top layer contains a large surface area which faces the sunlight to capture the maximum amount of light energy. Light travels though the thin outer layer of the leaf and to the chloroplasts inside.

- The middle layer contains many chloroplasts in each cell and is the site of photosynthesis.

- The bottom layer contains stomata that exchanges gases with the air.

∙ Stomata: Pores in the leaf that allow gas exchange – CO2 in and O2 out.

∙ Guard Cells: Cells that open and close the stomata.

∙ When the stomata are open, carbon dioxide enters the leaf and oxygen and water exit the leaf.

∙ Transpiration: The loss of water from plant leaves through openings called stomata.

∙ A plant usually wilts because more water is being lost than is being absorbed by the roots.

- Like stems, the veins of a leaf contain xylem and phloem. Xylem transports water to the leaf for photosynthesis and the Phloem delivers sugar (glucose) made during photosynthesis to the rest of the plant.

D. Seeds

1. Seeds develop after fertilization in the ovule of a flower. Seeds protect and provide nutrition for the new embryo that is inside. Fertilization is the union of an egg and sperm.

2. A seed is made up of 3 Parts: (1) The Embryo, (2) Stored Food, and (3) A Seed Coat that surrounds and protects the young plant.

3. Plants that reproduce using seeds have advantages over seedless plant in some environments.

- When a seed begins to grow, the young plant is nourished by the food stored in the seed. It can use that stored food until it is able to make all the food it needs by photosynthesis.

- Under what conditions can a seed be an advantage?

4. Plants grow through 4 distinct stages: Seed → Seedling → Young Plant →

Adult Plant with flowers

4. Germination: The process by which a dormant seed begins to sprout and grow into a

seedling under the right growing conditions.

- The seed begins to differentiate into three major sections. Water is taken in

by the developing plant and pressure forces the plant upward.

∙ Seeds need water to sprout. Before sprouting, seeds absorb water. They take in so much water that the force of the water pressure pushes open the seed coat. The force of water pressure “inflates” the emerging shoot of some plants. The force of the shoot straightening pulls the seed leaves (cotyledons) above ground.

∙ Turgor Pressure: The pressure exerted by water inside the cell

against the cell wall.

∙ Wilting: Refers to the loss of rigidity of non-woody parts of plants. This occurs when the Turgor pressure in plants cells falls towards zero, as a result of diminished water in the cells.

- Parts of a Developing Seedling

∙ Epicotyl: Becomes the leaf. Hypocotyl: Becomes the stem.

∙ Radicle: Becomes the root.

5. Types of seeds

- Monocots: A group of flowering plants characterized by having only one cotyledon in the seed. (stored food is one part like a corn kernel)

- Dicots: A group of flowering plants characterized by having two photosynthetic cotyledons in the seed. (stored food split into two parts like a peanut or lima bean)

E. Flowers

- Flowers help plants reproduce. Most are adapted to attract pollinators – by smells and colors. Others have dull and very small flowers (grasses & weeds) and are often wind pollinated so they do not require the attraction of a pollinator.

- Flowers are the reproductive organ of the plant. There are both male and female structures which produce gametes (egg & sperm). Pollination allows fertilization to take place and the new embryo develops into a seed.

F. Fruits

- Fruits are the ripened ovary of what once was a flower. Fruits can be fleshy (like an apple) or dry (like a walnut). Ripening of the fruit can help with dispersement of the seeds.

- Fruit contain many nutrients to support the development of the seed into a seedling. This is why they contain sugars and are often sweet.

∙ Animals enjoy them for their taste and eat them for their nutrition. They then play a role in dispersing the seeds that pass through their digestive system.

∙ Animals eat fruits and spread the seeds away from the plant. The animal

benefits from eating the fruit and the plant in turn benefits if the seed is

dropped somewhere that it can grow (mutualism).

IV. Photosynthesis

- Plants make their own food through photosynthesis. During photosynthesis, radiant energy from sunlight is converted to chemical energy (ATP) stored in the sugar glucose. Glucose is formed from carbon dioxide and water. Carbon dioxide comes from the air. It enters the plant through stomata in the leaves. Water enters the plant through the roots. Xylem brings the water to the leaves, where photosynthesis takes place.

- Photosynthesis: The process by which some organisms use sunlight, carbon dioxide, and water to produce sugar and oxygen.

A. Capturing Light Energy

- Plants capture light energy and use that energy to make glucose. Chloroplasts are membrane bound organelles containing chlorophyll. There are found in the middle layer of the leaf and are the site of photosynthesis.

∙ Grana: Stacks of inner membrane in chloroplasts that contain the green pigment, chlorophyll.

∙ Plants look green because chlorophyll reflects green light.

B. Making Sugar

- The light energy absorbed by chlorophyll is used to break water (H2O) into hydrogen (H) and oxygen (O). The hydrogen is then combined with carbon dioxide (CO2) to make a sugar called glucose (C6H12O6). Oxygen is given off as a byproduct.

(reactants) 6 CO2 + 6 H2O + Light Energy → C6H12O6 + 6 O2 (products)

- The chemical energy stored in food molecules (made in chloroplasts) is used by plant cells to carry out their life processes. Within each living cell, glucose and other food molecules are broken down in the mitochondria.

∙ Cellular Respiration: The process of producing ATP in the cell from oxygen and glucose: releases carbon dioxide and water.

(reactants) C6H12O6 + 6 O2 → CO2 + 6 H2O + ATP (products)

C. How does the plant obtain each of the Reactants need to do photosynthesis.

- Carbon Dioxide: This is absorbed from the air through the stomata on the leaves of

the plant.

- Water: This absorbed from the ground through roots hairs and into the xylem

“pipes” of the plant.

- Sunlight: This is captured from the air through the chlorophyll in the chloroplasts in

the middle layer of leaf’s cells.

D. Where are the Products from Photosynthesis then released or stored?

- Glucose: This is sent through the phloem “pipes” to all cells to be used for the

process of cellular respiration.

- Oxygen: This is release through the stomata of the leaf and into the air.

- Flowers usually contain the following parts: Petals, Stamens, Pistil(s)

∙ Petals: The often colorful structure on a flower that is usually involved in attracting pollinators.

- Animals help flowered plants reproduce by transferring pollen from one plant to another.

- Flowers that have brightly colored petals and aromas usually depend on animals for pollination.

- Flowers without bright colors and aromas usually depend on wind to spread them.

∙ Stamens: The male reproductive structure in the flower that consists of a filament topped by a pollen-producing anther.

∙ Pistils: The female reproductive structure in a flower that consists of a stigma, a style, and an egg-producing ovary.

- Ovary: The rounded base of the pistil.

- If fertilization occurs, the ovary develops into a fruit. Fruits may contain one or more seeds.

II. Life Cycles of Plants

- Plants lead a double life – all plants have two stages in their life cycle:

1. Sporophyte: A stage in a plant’s live cycle during which spores are produced.

∙ Spores: Reproductive cells that grow into gametophytes.

2. Gametophyte: A stage in a plant’s life cycle during which eggs and sperm are produced.

∙ Gametes: Sex cells (egg and sperm)

- An egg that is fertilized by a sperm can grow into a sporophyte, completing the cycle.

- The 4 main types of plants have different life cycles.

1. The Life Cycle of Mosses

a. The male gametophyte produces sperm

b. The sperm fertilizes the egg at the tip of the female gametophyte. The fertilized egg grows into the sporophyte, which grows on top of the gametophyte.

c. The sporophyte releases spores.

d. Spores grow into green, leafy gametophytes.

2. The Life Cycle of Ferns

a. The gametophyte stage of most ferns produces both eggs and sperm.

b. The sperm swim to an egg and fertilize it.

c. The sporophyte grows from the fertilized egg. Spore sacs under the fronds produce spores.

d. The spore sacs release spores that grow into the small, heart-shaped gametophytes.

3. The Life Cycle of Gymnosperms

a. The sporophyte stage of most gymnosperms produces both male and female cones. Sperm produced by gametophyte tissue within a male cone is packaged into pollen.

b. The egg is produced by gametophyte tissue in a female cone. The egg is fertilized inside the cone by sperm from pollen.

c. The fertilized egg is encased in a seed.

d. The sporophyte stage grows from the seed.

4. The Life Cycle of Angiosperms

a. The sporophyte stage of most flowers has both pistils (female reproductive parts) and stamen (male reproductive part).

b. The pistil produces pollen. Inside the pollen, sperm is made by gametophyte tissue.

c. The egg is produced by gametophyte tissue within the stigma. The fertilized egg is enclosed in a seed.

d. A fruit surrounds the seed, which grows into a mature sporophyte.

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Is That A Fact: Some flowering plants have a type of surface protector that functions much like sunscreen lotion. Alpine flower at high elevations produce purple pigments in their leaves to shield them from the damaging effects of ultraviolet light. The pigment allows in sunlight that is needed for photosynthesis but filters out harmful UV rays.

Misconception Alert: A few plants, called saprophytes, do not make their own food. Saprophytes lack chlorophyll and are usually white. They parasitize other plants by absorbing nutrients through their roots.

Is That A Fact: Some of the same factors that encourage the development of peat – high acidity and low oxygen – have preserved the bodies of people who died in bogs. Preserved bodies have been recovered from bogs in Europe and in Florida. Some of the bodies are 2,000 years old.

Is That A Fact: The deepest roots ever discovered belonged to a wild fig tree in South Africa. The roots were 122 m deep.

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