y,

•.ft^WS

-I]

4Lesson113il

^^

§i

t

ESSENTIAL QUEST!ON

How do plantsstay aliv&?

*<^,,

II

»By the end of this lesson, youshould be able to describe the

processes through which plantsobtain energy, reproduce, andrespond to their environments.

!1

^/;

S&..

I'll

mItti

itUWNI ga

»»;(l( s;

I

s ma>±£

i,1

^1•I

« Iili§

*ll

Ill

a

120 Unit 2 Earth's Organisms^

^'S/^'Ms:wi sS-

^•s^.^"

"si^s:ffsw"

'n

Lesson Labs"ft

^ixsie

^^̂^

Hfca

K

^^

s333

•^3'*s3•a5

^^^^^•"'9'''3•>a5•--?-3

.-^

;ari»

'-*

»

s

-a*

^•aai

•*5

a5§i

•^1.1'*(@

35

•--)

•5

^

s

s

33

--^'̂

sa

ittlsS^: -

Quick Labs

• Investigating Plant Pigmentsi • Observing Stomata

Exploration Lab• Fertilization In Angiosperms

J

A-a^-i Ewgag& Your Brain1 Identify Read over the following vocabulary

terms. In the spaces provided, place a + if youknow the term well, a - if you have heard theterm but are not sure what it means, and a ? ifyou are unfamiliar with the term. Then write asentence that includes one of the words you aremost familiar with.

cellular respiration

.transpiration

.tropism

2 Describe Finish the caption for this photo.

The vine responds to the wire by

pollination

Sentence using known word:

%>•s.

»

&• :m

sIJ;••;' K^a ^tg

ff

s ss itSK

^•^^RII^I'

3 Synthesize You can often define an unknownword if you know the meaning of its word parts.Use the word parts and sentence below to makean educated guess about the meaning of theword photosynthesis.

Word part Meaning

photo- light

synthesis putting together

Example sentence:Plants die without sunlight because they areunable to carry out photosynthesis.

photosynthesis:

Vocabulary Termscellular respiration • stimuluspollination • transpirationstamen • tropismpistil • dormant

4 Apply As you learn the definition of eachvocabulary term in this lesson, createyour own definition or sketch to help youremember the meaning of the term.

r.

t,

Lesson 4 Plant Processes 121

II!1-

Ill

IIIf

"Ill

I!

l'!ll:Ill

II

f.

Ill11 ill!

l nil

lEil

1131Ill

I!11111lllliliil

h

Ill! It

ill

Ilij;i

Fnelerl Rv theHow do plants obtain and useenergy?Plants, like all living things, need energy to survive. But plantsdon't exactly "eat" to get energy. Plants get energy from sunlightduring the process of photosynthesis.

Plants Capture Light Energy in ChloroplastsPlants use photosynthesis to change light energy to chemicalenergy in the form of sugar. Unlike animal cells, plant cellshave organelles called chloroplasts [KLOHR*uh*plasts], wherephotosynthesis takes place. Chloroplasts are made up of twomembranes that surround stacks of smaller, circular membranes.These smaller membranes contain chlorophyll, which is a greenpigment. Chlorophyll absorbs light energy from the sun.

Sunlight is made up of various wavelengths of light. Differentwavelengths of visible light are seen as different colors. Chlorophyllabsorbs many wavelengths, but it reflects more green light thanother colors of light. As a result, most plants look green.

I

II

ii

§1; !!,»,

&ti ^ W^iljze fti

s

5 Describe Fill in the captions to describehow plants obtain energy from sunlight.

;'1(1EI

•

f.MLightenergy fc

r;i

^I Carbondioxideil Oxygen

.!|

Chloroplasts Use Light Energyto Make SugarThe light energy captured in chloroplasts ischanged and stored in the bonds of a sugarcalled glucose. In the same process, oxygen gas isreleased. Many chemical reactions occur duringphotosynthesis. The process can be summarizedby the following equation:

Photosynthesis

(.CO, + W,0 — —— ^—> C^O, + GO,

This equation shows that light energy is used tochange six molecules of carbon dioxide and suemolecules of water into one molecule of glucoseand six molecules of oxygen gas.

Chloroplast fc

Mitochondria Release Energyfrom SugarIn plants, extra glucose is stored as starch orchanged to other types of sugar such as fructoseor sucrose. Cellular respiration [SEL*yuh«luhrres*puh*RAY*shun] is the process by which cellsuse oxygen to release the stored energy from thebonds of sugar molecules. This process occurs inmitochondria. Cellular respiration also producescarbon dioxide and water.

11111

Cellular respiration

c^u°^ + (ooz —>^CO^+ (oM^O + energy

In cellular respiration, one molecule of glucoseand sue molecules of oxygen are changed into sixmolecules of carbon dioxide and sue molecules

of water. The reaction changes the energy insugar into energy that can be used to power cellprocesses.

6 Relate How is cellular respiration the reverse ofphotosynthesis?

II

Ill

-r

nns^

3t

Plant cell

gt3^

gt:

Plant cells have organelles called chloroplasts,where photosynthesis takes place. These organellescontain a pigment called

that absorbs light.

I

1!'-

Mitochondrion fe^w^^^w^^^^'1'

Cellular respiration occurs inorganelles called mltochondria.Cellular respiration uses oxygen torelease energy from glucose. It alsoreleases

and

:~^

&-^fc

)a c

What are the phases of a plant's lifecycle?All plants complete their life cycles by alternating between twophases, the sporophyte phase and the gametophyte phase. Thesetwo phases look different from each other.

In one phase, plants called sporophytes [SPOHR*uh*fyts]produce spores by meiosis. Meiosis is a process of cell divisionin which each daughter cell receives half the chromosomes ofthe parent cell. The products ofmeiosis in plant sporophytes arespores. The spores are then released.

Under the right conditions, spores grow into plants calledgametophytes [guh*MEET«uh«fyts]. Female gametophytes makeeggs. Male gametophytes make sperm. When a sperm fertilizes anegg, they combine to form an embryo. The embryo develops into aseed, which is released and can grow into a new sporophyte.

.'-^.a

.!

f

ili

i^i Visualize Iti7 Contrast Use the diagram to explain how spores differ from seeds.

1>m

m

I.

sporophyte'^ilj»-l

SNJ;;

seedw.»1

n

A sperm andan eggcombine to produce a seedm

Sswes are producedi

How do seedless plantsreproduce?The gametophyte generation in plants makeseggs and sperm. In seedless plants, sperm arereleased in the presence of water. Sperm havewhip-like tails. The sperm swim to the eggs andfertilize them. The fertilized eggs then grow intosporophytes.

Some seedless plants, such as mosses, havea visible gametophyte phase. The short, denseplant you think of as moss is the gametophyte.Sometimes you can also see the sporophytes ofmoss if you look closely. They are thin, brownstems topped by a small, brown capsule.

How do seed plantsreproduce?The sporophyte is what you see in seed plants.In most seed plants, the sporophyte makes twotypes of spores, male and female, that grow intomicroscopic male and female gametophytes.The male gametophyte is pollen, a tiny structurein which sperm form. Pollen may be carriedby wind, water, or animals to the female plantreproductive structure. The female gametophytedevelops inside an ovule, which is part of thesporophyte. Within the ovule the gametophyteproduces eggs. Pollination happens when pollenlands on the female plant reproductive structureand fertilizes the eggs. The fertilized egg developsinto an embryo and the ovule becomes the seed.

8 Diagram Fill in the Venn diagram to compareand contrast the way seedless and seed plantsreproduce.

Kepro^yction ofSeeAless plant?

KeprotJuctionof yee

ii!

I

II

li

•!il

li

131Ill I

!i

3!;

K!1!

I

I

iI!

jliu>

11'II

It"

EJIJll!

I

^

»»

IICTt

I III!'l:ilill

l»t>l

l»tl,l

l*h|

1

.h

w

How do flowering plants reproduce?In flowering plants, sexual reproduction takes place inside theflowers. Flowers are reproductive structures that have specializedleaves called sepals and petals, which often attract animalpollinators such as insects.

A stamen is the male reproductive structure of flowers. At thetip of each stamen is an anther, where pollen is produced. A pistil isthe female reproductive structure of flowers. When a pollen grainreaches the tip of the pistil, called the stigma, pollination occurs. Apollen tube grows down through the pistil into the ovary. Withinthe ovary are one or more ovules containing eggs. Sperm traveldown the tube, into the ovary, and fertilize the eggs.

A fertilized egg develops into an embryo, a tiny, undevelopedplant. The ovule develops into a seed that surrounds and protectsthe embryo. The ovary becomes a fruit, which protects the seedsand helps seeds to spread. When conditions are right, seeds willsprout and grow into new plants.

^Visualize It!9 Identify Circle the two labels of gametophyte structures in the illustration.

0 Pollen grains land on thepistil and begin to growpollen tubes.

Stamen

Pistil

-^

&F .^

<

^

Sperm travel downpollen tubes andfertilize the eggs.

•Sperm

Pollen tube

•Ovary

Egg (inside ovule)

\

n

Each ovulewithin theflower's ovarycontains afertilized egg.

Each seed containsa tiny plant. If a seedsprouts, or begins togrow, it will becomea new plant.

0 Petals andstamens fallaway.

The ovary becomes the fruit,and each ovule becomes aseed. Eventually, the fruit ripens,and the seeds are dispersed.

126 Unit 2 Earth's Organisms

II

's.

IIi

II

How do plants reproduce asexually?Most plants can also reproduce asexually. Asexual reproductionallows a plant to reproduce without seeds or spores. Duringasexual reproduction, part of a parent plant, such as a stem or root,produces a new plant. Some examples of structures that plants useto reproduce asexually include plantlets, tubers, and runners.

• Plantlets are tiny plants that grow along the edges of aplants leaves. These plantlets fall off and grow on their own.

• Tubers are underground stems that store nutrients and cangrow into new plants. A potato is a tuber. Each "eye" cangrow into a new plant.

• Runners are above-ground stems that can grow into newplants. Strawberries send out lots of runners.

11 Apply Write a play thatcompares and contrasts theresults of sexual and asexualreproduction in plants.

IIill;ffi,s

^ Visualize ffi10 Label Under each example of asexual reproduction,

write the type of structure used for this purpose.

y (/ying t^emateriol? ff'ored in?i

II

I

jl:l

-I I

Iti'l^l,

II

I^

«> Ks

s's8»^ ».

rnf

a

y

?

^

V/hen plant? \ofe 3moye Water t^an tA»ev

obyorb, they l^ift3

When stomato Qre open,plant? can obtain carbonA'fox'i^e for fhol'osynthesi?an

Iis^.

B§&

I

E

't

iI

Q

! ActivaReading

13 Identify As you read, underlinethe effect of phototropism.

By GrowingPlant growth in response to a stimulus is called a tropism. Planttropisms are controlled by plant hormones. Hormones arechemical messengers that cause changes in cells.

A change in the direction of plant growth in response to lightis called phototropism [foh«toh*TROH«piz*uhm], as shown in thephoto on the left. Hormones build up in cells on the shaded side ofthe stem, causing these cells to lengthen. The lengthening of thesecells makes the stem bend in the direction of the light.

A change in the direction of plant growth in response togravity is called gravitropism [gravih«TROH*piz*uhm], shown onthe right. Most stems grow upward, away from the pull of Earthsgravity, and most roots grow downward, toward the pull of gravity.

^Visualize Iti14 Label Draw an X next to the side of the stems with shorter cells.

Plontyben

^(SM®'1i;;*v.

-«w;

"fl«

i

I

ni

:ll

!•»

m,

m\

Wtti

mm

E!, N'

Itl

V: "Is;

1.1

w W'll»tk1..1

I,1

.-^^» ,^^.y.t.',<

tl«

s.vm

.:'^ltaava:m.?

as»& (.I ^vfi ^ \

••iS®'wne ]^WK-IW»'WT.^w^ywgi^jg«!^g^np^agi^:».:.»|(b,,,..^

'SiSSiSfSi^

B$,

Sl^IW^•,£^y^S^M?';ltS%8S

':rt,l«?^'S3s:'S»"'W$ii' ? ^'M 's-vw t.i.s-rsfi%gt^V^SSx^SiQSiM'..'^'^QissiSQSSSSs^SS'&SSJ

'f:f3v-^