PHOTOSYNTHESIS
• The sun is the source of energy for most living things
• Example:
• Plants get energy from the sun
• Cow gets energy from the plants
• Human gets energy from the cow
• Plants make their own food
• Organisms that make their
own food are called
autotrophs
• Organisms that cannot make
own are heterotrophs
• The processes by which a
cell captures energy in
sunlight and uses it to make
food is called photosynthesis
their
• Process of Photosynthesis
• Sun’s energy captured
in the chloroplasts and
absorbed by
chlorophyll
• Water and carbon
dioxide chemically
react to produce
sugars C6H12O6 and oxygen O2
• Sugar is used to carry
out cell functions
• Oxygen is given off as
a waste product
CAPTURING THE SUN’S ENERGY
•
•
•
•
The first stage of photosynthesis is
capturing the sun’s energy
In plants, this energy process occurs
in the leaf cells
Chloroplasts are organelles in those
cells that contain chlorophyll
The green color comes from the
chlorophyll which absorbs light
Stage 1
Stage 1
•
•
•
Chlorophyll functions like solar “cells”
Solar cells capture light energy
and uses it to power devices
Similarly, chlorophyll captures light
energy and uses it to power the
second stage of photosynthesis
•
In the next stage of
photosynthesis, the cell
uses the captured
energy to produce
sugars
Stage 2
• Some of the sugars are used for food
• The cells break down the sugar molecules to
release the energy they contain
• This energy can then be used to carry out the
plant’s functions
• Some sugar molecules are
converted into cellulose
• Other sugar molecules may
be stored in the plant’s cells
for later use. When you eat
potatoes or carrots, you are
eating the pant’s stored energy
•
The cell needs two raw
materials for this stage:
•
•
•
•
Stage 2
Water and carbon
dioxide
Water is absorbed by
the roots and moves up
to the plant’s leaves
Carbon dioxide enters
the plant through small
openings on the
undersides of the leaves
called stomata
Once in the leaves, the
water and carbon dioxide move into the chloroplasts
The photosynthesis equation
The events of photosynthesis can be summed up by the following
chemical equation:
light energy
6CO2 + 6H2O
Carbon
water
dioxide
6 Carbon atoms
18 Oxygen atoms
12 Hydrogen atoms
C6H12O6 + 6O2
sugar
oxygen
No atoms are
lost or gained
in the process
6 Carbon atoms
18 Oxygen atoms
12 Hydrogen atoms
•
•
Through the process of photosynthesis, plants produced almost
all the oxygen in Earth’s atmosphere
Animals use oxygen which is the waste product of plants and
plants use carbon dioxide which is the waste product of animals
Animals give off
carbon dioxide
Plants give off
Oxygen
RESPIRATION
• Before food can provide your body with
energy, it must pass through your digestive
system
• There, food is broken down into molecules
• These molecules then pass into your
bloodstream
• Next, the molecules travel to all the cells in
your body
• Inside the cells, the energy in the molecules
is used to perform all your body’s functions
ENERGY
ENERGY
• Because living things need a continuous supply of energy, the cells of all
living things carry out respiration continuously
• Photosynthesis—carbon dioxide and water produce sugars and oxygen
• Respiration—sugars and oxygen produce carbon dioxide and water
• Photosynthesis and Respiration can be thought of as opposite processes
ANIMALS
PLANTS
• Living organisms get energy
from sunlight or food and
“save” it in the form of
carbohydrates including
sugars and starches
• When cells need energy, they
“withdraw” it by breaking
down the carbohydrates in
the process of respiration
• Like photosynthesis, respiration is a two-stage process
• The first stage takes place is the
cytoplasm
• There, molecules of sugar are
broken down into smaller
molecules
• Oxygen is not involved, and
only a small amount of energy
is released.
• The second stage of respiration takes place in the
mitochondria
• There, the small molecules are
broken down into even smaller
molecules
ENERGY
• These chemical reactions require
oxygen, and they release a
great deal of energy
• This is why the mitochondria are
called the “powerhouses”
of the cell
ENERGY
• The energy released by the mitochondria is stored as
chemical energy that is immediately ready to be used by
the cells
• Two other products of respiration are carbon
dioxide and water
• The carbon dioxide diffuses
out of the cell
ENERGY
• When you breathe in, you take
in oxygen
• When you breathe out,
you release carbon dioxide and
water which are the waste
products of respiration
ENERGY
The respiration equation
Although respiration occurs in a series of complex steps,
the overall process can be summarized in the following
equation:
C6H12O6 + 6O2
6CO2
+
Sugar
oxygen carbon dioxide
6H2O + ENERGY
water
Fermentation
• Some cells are able to obtain energy
without using oxygen
• For example, single celled organisms
living under water without oxygen
• These organisms obtain their energy
through fermentation, a process that
does not require oxygen
• The amount of energy released during fermentation lower than the
amount released during respiration
Alcohol Fermentation
• Yeast breaks down sugar to produce alcohol,
carbon dioxide, and small amount of
energy
• The products of alcoholic fermentation
are important to bakers and brewers
• Carbon dioxide produced by yeast
creates air pockets in bread dough,
causing it to rise
• Carbon dioxide also causes the
bubbles in
alcoholic
drinks such
beer and
sparkling
wine
as
Lactic acid fermentation
• Another type of fermentation takes place at times
in your body
• You run as fast as you can for as long as you can
and no matter how hard you breath, your muscle
cells used up the oxygen faster than it can
be replaced
• Because your cells lack
oxygen, fermentation
occurs to produce energy
• One product of fermentation
is lactic acid
• When lactic acid builds up,
you feel pain in your muscles
CELL DIVISION
• Cells grow and divide over and over
• The regular sequence of growth and division
that cells undergo is known as the cell cycle
• During the cell cycle, a cell grows, prepares
for division and divides into two new cells
called "daughter cells"
• Each of the daughter cells begins the cell
cycle again
•
•
•
•
The cell cycle is divided into three main stages:
Interphase
Mitosis and
Cytokinesis.
Interphase
• Interphase is the period before cell division
• The first part: the cell grows to full size
• Produces new ribosomes and
enzymes
• Copies made of mitochondria and
chloroplasts
• The second part: an exact copy of
the DNA is produced in the nucleus
in a process called replication
• The chromatin appears as a dense mass within the nucleus
• DNA holds all the information that the
cell needs to carry out its functions
• At the end of DNA replication,
the cell contains two identical sets
of DNA
• Once the DNA has replicated
The cell produces structures that
it will use to divide into two new cells
At the end of interphase, the cell is
ready to divide
Mitosis
• Scientists divide mitosis into four phases:
prophase, metaphase, anaphase, and
telophase
• During prophase, the threadlike chromatin
in the nucleus condenses to form double-rod
structures called chromosomes
• Each chromosome has two rods because the
DNA replicated
• Each identical rod in a chromosome is called a
chromatid The two chromatids are held
together by a structure called a centromere
• As the cell progresses through metaphase, anaphase, and
telophase, the chromatids separate from each other and move
to opposite ends of the cell
• Then two nuclear envelopes form around the new chromosomes
at the two ends of the cell
Cytokinesis
• Cytokinesis is the final stage of the cell
cycle
• The cytoplasm divides and the
organelles are distributed into each
of the two new cells
• Cytokinesis usually starts at the same
time as telophase
• When cytokinesis is complete, two
new cells, or daughter cells are formed
• Each daughter cell has the same
number of chromosomes as the
original parent cell
• At the end of cytokinesis, each cell enters
interphase, and the cycle begins again
• Cytokinesis in animal cells
• During cytokinesis in animal
cells, the cytoplasm pinches
into two cells
• Each daughter cell gets
about half of the organelles
• Cytokinesis is different in plant cells
• A plant cell’s rigid cell wall cannot squeeze
together
• A cell plate forms across the parent cell
• The cell plate gradually develops into new
cell membranes between the two daughter
cells
• New cell walls then form around the cell
membranes
THE STRUCTURE OF DNA
• DNA replication ensures that each daughter
cell will have the genetic information it
needs to carry out its activities
• Before scientists could understand how DNA
replicates, they had to know its structure
• In 1952, Rosalind Franklin uses an x-Ray
method to photograph DNA molecules
• Her photographs helped scientists figure out
the structure of DNA in 1953
• The strands of a DNA molecule look like a
twisted ladder
• The two sides of the DNA ladder are made up
of molecules of sugar called deoxyribose and
phosphates
• Each rung is made up of a pair of
molecules called nitrogen bases
• Nitrogen bases are molecules that
contain the element nitrogen and other
elements
• DNA has four kinds of nitrogen bases:
•
•
•
•
Adenine
Thymine
Guanine, and
Cytosine
• The capital capital letters A, T, G, and C
are used to represent the four bases
Replication of DNA
• DNA replication begins when the two sides of the DNA molecule
unwind and separate, somewhat like a zipper unzipping
• The molecule separates between the paired nitrogen bases
• Nitrogen bases that are floating in the
nucleus connect with the bases on each
half of the DNA molecule
• The bases on one side of the ladder then
connect with the bases on the other side
• Adenine (A) only pairs with thymine (T)
• Guanine (G) only pairs with cytosine (C)
• This pairing pattern is the key to
understanding how DNA replication
occurs
• The order of the bases in each
new DNA molecule exactly
matches the order in the
original DNA molecule
• Once the new bases are
attached, two new DNA
molecules are formed
CELL DIFFERENTIATION
• When a cell divides by mitosis, it produces two daughter cells
that are identical to it and each other
• Then, how do cells in multicellular organisms become different
from one another?
• Differentiation is the process by which cells carry out specialized
functions
• As cells differentiate, they become different from one another
• They also form groups of other, similarly specialized cells
• These groups then form tissues and organs
Differences in Structure
• Multicellular organisms
begin their lives as one
cell
• After three mitosis cycles
differentiaton begins
• The single cell becomes
an organism with
specialized structures
• For example,
• A single plant cell can differentiate into:
• leaf cells, transport cells and root cells look different.
• As cells differentiate their organelles
differentiate also to carry out different
functions
• For example,
• Plant leaves contain cells that carry out
photosynthesis
• Root cells are underground and do not
carry out photosynthesis
• Leaf cells have many chloroplast to
capture sunlight
A Root Cell
• Root cells have no
chloroplast but have
more vacules to
absorb water from the
soil
Nucleus
•
When cells differentiate, they become organized
•
Similar cells group into tissues that carry out specific functions
•
For example, Muscle cells in animals group into long strands of muscle tissue
that move legs or arms
Skeletal Muscle
xylem
Voluntary Muscle
Striated Muscle
Smooth Muscle
Cardiac Muscle
•
Groups of tissues combine to form organs, such as leafs of a plant or the
heart of an animal
LEAF
HEART
Epidermal Tissue
Phloem Tissue
Cardiac Muscle Tissue
Nerve Tissue
Blood Tissue
Chlorophyll
•
Groups of organs form organ systems, such as the digestive system
Moo
Circulatory
System
Digestive System
Stomach
Intestines
Heart
Arteries
Veins
Pancreas
• As differentation continues, increasing specialization occurs
• For example,
• The retina of your eye
consists of 7 different types
of cells
• Each type of cell has a
specialized job to do
• The cells of your retina
differentiated early in your
development before you
were born
•
During an organism’s development, the instructions that
determine how its cells will differentiate are coded in the DNA in
each cell’s nucleus
•
When and how much they differentiate depends on their DNA
and the type of organism
•
Some cells differentiate completely during an organism’s
development
•
Other cells do not specialize until later in the life of an organism.
DIFFERENTIATION IN ACTION
Cell Differentiation Among
Animals
•
Many adult animals such as insects
and some crustaceans and reptiles
can grow a tail to replace a lost
one
•
Cells at the point of the injury
differentiate, forming new muscle,
bone, blood, and nerves
• The replacement of lost body parts
does not occur in humans
• Once human cells differentiate,
they usually lose the ability to
become other types of cells
• Humans do produce certain cells
called stem cells that can
differentiate throughout life
• Stem cells respond to specific needs
in the body by becoming
specialized
• For example,
• You need a constant supply of
new blood cells to your replace
older cells
• Everyday, stem cells produce a
steady supply of blood cells
Cell Differentiation Among
Animals
•
Cells differentiate in plants much
the same way they do in animals
•
Differentiated cells become root,
stem, and leaf cells
•
Cells continue to differentiate
within each kind of organ
•
For example, some cells in the
plant’s stem specialize as tubes
that transport food and water
throughout the plant
• Many plants grow throughout their lives
• Certain cells in the roots and stems
increase size by rapid cell division and
differentiation
• Differentation can lead to growth of
new roots, stems, and leaves
• For example,
• A leaf of an African violet plant that is cut off
and put into water will begin to differentiate
into root cells and stem
cells, and a whole new
plant will grow
• Gardeners use this
technique to create many
plants from one original plant