Plants!!! 7th Grade Science

What is a plant? Autotrophs Eukaryotes Plant Cells Photosynthesis Use energy from the sun to make their food Eukaryotes Many cells organized into tissues Tissues = groups of similar cells that performs a specific function Plant Cells Cell wall = boundary that surrounds the cell membrane and separates the cell from the environment Cell walls made of cellulose, which makes them rigid Chloroplasts Vacuole = large storage area for water, food, wastes; expands and shrinks depending on how much water is in the cell

Where did plants come from? Scientists study the fossil record for clues Oldest plant fossils are about 400 million years old Scientists study chlorophyll Chlorophyll comes in different forms Different forms have slightly different chemical structures Plants and green algae have the same form of chlorophyll, so scientists infer that ancient green algae were the ancestor’s of today’s plants

How do plants survive on land? Obtain/retain water and nutrients from their surroundings Plants have adaptations that allow them to get water and nutrients from the soil Plants have adaptations to stop the water in their cells from evaporating into the air Common adaptation is the cuticle, a waxy, waterproof layer that covers the plant’s leaves Transport materials throughout the plant Food made in the top part of a plant, water absorbed through the bottom part, plant has to have vascular tissue which can move food and water throughout the plant Reproduce All plants undergo sexual reproduction Fertilization occurs when a sperm cell unites with an egg cell Fertilized egg = zygote

Plants have a complex life cycle! Two different stages/generations Stage 1 = Sporophyte Plant produces spores Spores are tiny cells that can grow into new organisms Spores develop into stage 2 Stage 2 = Gametophyte Plant produces two kinds of sex cells Gametes (sex cells) are sperm cells and egg cells P. 307

Plant Life Cycle Sperm cell and egg cell join to form the zygote Zygote develops into a sporophyte Sporophyte produces spores Spores develop into gametophyte Gametophyte produces sperm and egg cells

Nonvascular Plants Nonvascular plants are plants that are low-growing and lack vascular tissue Examples of nonvascular plants include mosses, liverworts, and hornworts Remember that vascular tissue transports water and nutrients throughout a plant, so nonvascular plants don’t have this Nonvascular plants are only able to transport material from one cell to a cell directly next to it, so materials do not travel far or quickly These plants obtain water and nutrients from their surroundings directly Need to have enough water nearby so that sperm cells can swim to the egg cells during reproduction

Mosses Over 10,000 species of moss, can grow in many places Picture p. 316 Moss that we think of is the gametophyte generation Rhizoids = thin, root-like structures that anchor the moss and absorb water and nutrients Sporophyte generation grows out of the gametophyte, consists of a slender stalk with a capsule at the end, capsule has spores

Moss!

Liverworts and Hornworts 8,000 species of liverworts Liverworts named for the shape of the plant, which looks like a human liver Liverworts grow flat along the ground, in moist soil or near streams Fewer than 100 species of hornworts Slender, curved structures grow out of the gametophytes – this is the sporophyte, which looks like a horn Hornworts live in moist soil

Liverworts and Hornworts

Seedless Vascular Plants This category includes ferns, club mosses, and horsetails Two characteristics in common – vascular tissue and the use of spores in reproduction Vascular tissue allows these plants to transport nutrients and water Vascular tissue also strengthens and stabilizes the plant’s body Grow in moist surroundings, where spores can grow into gametophytes and there is enough water available for fertilization to occur

Ferns 12,000 species of ferns Ferns have true roots, stems, and leaves Stems are underground, leaves grow upward from sides of the stem, roots grow downward from stem Roots anchor the fern to the ground and absorb water and nutrients Fronds = fern’s leaves, fronds are divided into many smaller parts Upper surface of each frond has a cuticle Developing fronds curl at first, called fiddleheads, uncurl as the frond develops

Ferns

Ferns Fern that is familiar to us is the sporophyte generation Spores develop on the underside of fronds Wind and water can carry spores great distances If a spore ends up in favorable conditions, it will grow into a gametophyte

Club Mosses Club mosses are small Not a true moss, club mosses have vascular tissue Ground pine/princess pine are examples of club mosses Grow in moist woodlands and near streams

Horsetails Only 30 species today Stems of horsetails are jointed Long, coarse, needle-like branches grow in a circle around each joint Small leaves grow flat against the stem just above each joint

Seed Plants Seed plants outnumber seedless plants more than 10 to 1 Seed plants share two characteristics Vascular tissue Xylem = vascular tissue that moves water from roots upward Phloem = vascular tissue that moves food from leaves downward Use seeds to reproduce Sporophyte generation = the plant we see, the gametophytes are microscopic

Seeds Seeds = structures that contain a young plant inside a protective covering Seed plants do not need water to reproduce After sperm cells fertilize the eggs, seeds develop All seeds have three parts Embryo = fertilized egg, develops from the zygote, has the beginnings of roots, stems, and leaves Stored food = uses this food until it’s big enough to make it’s own food, cotyledon Seed coat = protects embryo and food from drying out

Seeds

Seed Dispersal Seeds need light, water, and nutrients Seeds will sprout when they land in a suitable area Seeds are dispersed in many ways Animals Travel through digestive track and then are deposited Travel by hooking onto fur/clothes Water Seeds float along until deposited (remember deposition?) Wind Wind disperses lightweight seeds

Seed Dispersal

Germination Germination = early growth stage of the embryo Begins when seed absorbs water from environment, embryo uses stored food Roots grow downward, then leaves and stems grow upward Seeds dispersed far from parents have a better chance for survival because they’re not competing for resources

Germination

Leaves Most numerous part of plants, wide variety of shapes and sizes Leaves capture the sun’s energy and carry out photosynthesis (chloroplasts) P. 335 (Structure of a Leaf) Top and bottom layers of the leaf protect the cells in between Xylem and phloem are in the center of the leaf Stomata (carbon dioxide/oxygen gas exchange) Transpiration = the process by which water evaporates through the leaves

Leaves

Stems Stem has two functions – (1) carries substances between the roots and the leaves and (2) provides support for the plant and holds leaves up so they are exposed to the sun Wide variety of shapes and sizes (some are underground or very small, others are most of the plant!) Herbaceous vs. woody stems Woody stems have bark Annual rings (xylem)

Roots Roots = anchor a plant in the ground, absorb water and nutrients from the soil Taproot vs. fibrous roots P. 338 Taproot = one thick, long main root Fibrous roots = several main roots that branch off and form a mass of roots Root structure Root cap = contains dead cells, protects root from injury as it grows through the soil Root hairs = increase surface area to better absorb water/nutrients

Roots Taproot Fibrous Roots

Gymnosperms Gymnosperms = produce naked seeds (meaning their seeds have no protective covering) Many gymnosperms have needlelike leaves and deep-growing root systems 4 groups of gymnosperms Cycads Ginkgo Gnetophytes Conifers

Gymnosperms Cycad, ginkgo, and gnetophyte

Conifers Conifers = cone-bearing plants Pines, redwoods, cedars, hemlocks, junipers Evergreen plants = keep their leaves (needles) year-round

Gymnosperm Reproduction A single plant produces both male and female cones Male cones produce pollen, pollen contains microscopic cells that will develop into sperm Female cones contain an ovule, which contains an egg cell After fertilization, ovule develops into a seed p. 344 Pollen falls from a male cone onto a female cone, sperm cell joins with the egg cell in an ovule, fertilization occurs, zygote develops into the embryo part of the seed. Pollination = transfer of pollen from the male to the female reproductive structure.

Angiosperms Angiosperm = plant that produces seeds that are enclosed in a fruit, produce flowers and fruits Ovary = protected part of the plant where seeds develop, located within the flower Flower = reproductive structure of angiosperms p. 347 (structure of a flower) Petals and sepals Stamens = male reproductive part (anther, filament) Pistils = female reproductive part (stigma, style, ovary)

Parts of a Flower

Angiosperm Reproduction Pollen falls on stigma, sperm and egg cell join together in the ovule, zygote develops into the embryo part of seed Flower is pollinated when pollen falls on stigma, most pollination occurs by animals Ovary changes into a fruit – this is how seed dispersal occurs

Types of Angiosperms Monocots Dicots One seed leaf Grasses, corn, wheat, rice, lilies, tulips Either three petals or a multiple of three petals Long, slender leaves Two seed leaves Roses, violets, dandelions, oak trees, maple trees, beans, apples Flowers have four or five petals or multiples of four or five petals Leaves are wide

Plant Responses Tropism = plant’s growth response toward (positive tropism) or away (negative tropism) from a stimulus Touch = Thigmotropism Coiling vines Light = Phototropism Leaves, stems, and flowers grow toward light Gravity = Gravitropism Roots show positive gravitropism, they grow toward the pull of gravity So what about stems?

Plant Hormones Hormone = chemical that affects how the plant grows and develops Plant hormones control germination, the formation of flowers, stems, leaves, shedding of leaves, developing and ripening of fruit

Plant Review! All plants are autotrophic, eukaryotic, and multicellular All plants have a sporophyte and gametophyte generation Plants need the same things that ALL living things need! Photosynthesis (where does it occur? what is the formula?) Nonvascular, seedless vascular, and seed plants (gymnosperms and angiosperms) Plant responses = tropisms