Download Unit 2: Cell processes: transport, energy and division

Unit 2: Cell processes: transport, energy and division
1. The cell in its environment.
Cellular transport
All cells are surrounded by a cell membrane that
separates the cell from the outside environment. The
cell membrane is selectively permeable, which
means that some substances can pass through the
membrane while others cannot. Cells must let
needed materials (oxygen and food molecules)
enter. In contrast, waste materials must move out of
cells.
1.1 Diffusion
Diffusion is the main method by which small molecules move across the cell
membrane. Is the process by which molecules move from an area of higher
concentration to an area of lower concentration.
Diffusion of oxygen
Have you ever used a microscope to observe one-celled organisms in pond water?
These organisms obtain the oxygen they need to survive from the water around
them. Luckily for them, there are many more molecules of oxygen in the water
outside the cell than there are inside the cell. The cell membrane is permeable to
oxygen molecules. The oxygen molecules diffuse from the area of higher
concentration (the pond water) through the cell membrane to the area of lower
concentration (the inside of the cell).
Substances that can move into and out of a cell do
so by one of three methods: diffusion, osmosis,
or active transport.
Before Diffusion
After Diffusion
There is a higher concentration of
oxygen molecules outside the
cellthan inside the cell.
The concentration of oxygen molecules
is the same outside and inside the cell.
Effects of osmosis on cells
In osmosis, water diffuses through a
selectively permeable membrane
Water
molecules
Cell membrane
3. High Water Concentration Outside
Cell
1. Normal Red Blood Cell
Concentration of water
inside the cell is the same
as outside.
During osmosis water moves into the cell
2. Low Water Concentration
Outside Cell
Water moves out of the cell
during osmosis
1.2. Osmosis
Osmosis is the diffusion of water molecules through a selectively permeable membrane. Because cells cannot function properly without adequate
water, many cellular processes depend on osmosis. Water molecules move by diffusion from an area where they are highly concentrated through
the cell membrane to an area where they are less concentrated.
1.3. Active Transport
For a cell moving materials through the cell membrane by diffusion and osmosis do not require the cell to use
its own energy. The movement of dissolved materials through a cell membrane without using cellular energy is
called passive transport.
What if a cell needs to take in a substance that is present in a higher concentration inside the cell than
outside? The cell would have to move the molecules in the opposite direction than they naturally move by
diffusion. Cells can do this, but they have to use energy. Active transport is the movement of materials
through a cell membrane using cellular energy.
Active transport requires the cell to use its own energy, while passive trnasport does it.
Cells have several ways of moving materials by active transport:
Transport Proteins
Transport proteins in the cell membrane “pick up” molecules outside the cell and carry them in, using energy.
These proteins also carry molecules out of cells in a similar way.
Transport by Engulfing
Another method of active transport. First, the cell membrane surrounds and engulfs, or encloses, a particle.
Once the particle is engulfed, the cell membrane wraps around the particle and forms a vacuole within the cell.
The cell must use energy in this process.
Amoeba engulfing food
This single-celled amoeba is surrounding
a smaller organism. The amoeba will
engulf the organism and use it for food.
Engulfing is a form of active transport.
2. Cellular Energy
Every living thing needs energy. All cells need energy to carry out their functions, such as making proteins and transporting substances into and
out of the cell. Based on the way by which organisms and their cells obtain food and energy they can be divided into two groups:
Autotrophs: organisms that makes its own food. Plants and certain other organisms, such as algae and some bacteria, use the energy in
sunlight to make their own food through the process of photosynthesis.
Heterotrophs: organisms that cannot make its own food. Many heterotrophs obtain food by eating other organisms.
Autotrophs and Heterotrophs
Grass, which makes its own food during
photosynthesis, is an autotroph. Zebras and lions are
heterotrophs, because they cannot make their own
food.
2.1. Photosynthesis
It is a complex process. During photosynthesis, plants and some other organisms use energy from sun to convert carbon dioxide
(CO2) and water (H2O) into oxygen (O2) and sugars. The photosynthesis takes place in two stages:
Stage 1: Capturing the Sun’s Energy
This process occurs mostly in the leaves.
Chloroplasts in plant cells capture energy from
sunlight. These green organelles contain pigments
that absorb light. The main photosynthetic pigment
in chloroplasts is chlorophyll.
su
nli
gh
t
Cells containing chloroplasts.
Stoma
Stage 2: Using Energy to Make
Food
Cell use the captured energy to produce food.
In this stage cell needs two raw materials:
carbon dioxide (CO2) and water (H2O). In
plants the roots absorb water from the soil.
This water then moves up through the plant’s
stem to the leaves. Carbon dioxide is one of
the gases in the air. Carbon dioxide enters the
plant through small openings on the
undersides of the leaves calles stomata.
Once in the leaves , the water and carbon
dioxide move into the chloroplasts. Inside the
chloroplasts, water and carbon dioxide
combine in chemical reactions powered with
energy obtained during the first stage. These
reactions produce chemicals as products:
Sugars (glucose C6H12O6). Cells use energy
in glucose to carry out important cell functions.
The other product is oxygen (O2) which exits
the leaf through the stomata. In fact, almost all
oxygen in Earth’s atmosphere was produced
by living things through the process of
photosynthesis.
Carbon
dioxide
Oxygen
Water
The Photosynthesis Equation:
The events of photosynthesis can be summed up by the following chemical equation:
Light
energy
6 CO2
+
6 H2O
C6 H12 O6
carbon dioxide
water
a sugar
+
Notice that on the left the raw materilas are side of the equation and the products are
on the right side of the equation. Light energy, which is necessary for the chemical
reaction to occur, is writen above the arrow. What happens to the sugar (glucose)
produced in photosynthesis? Plant cells use some of the sugar for food. The cells
break down the sugar molecules to release the energy they contain. These energy can
be used to carry out the plant’s functions. Some sugar molecules are converted into
other compounds, such as cellulose. Other sugar molecules may be stored in the
palnt’s cells for later use. When you eat food from plants, such as potatoes or carrots,
you are eating the plant’s stored energy.
6 O2
oxygen
2.2. Respiration
Before food can provide your body with energy, it must pass through ypur digestive system. There, the food is broken down into small
molecules. These small molecules can then pass out of the digestive system and into your bloodstream. Next, the molecules travel through the
bloodstream to the cells of your body. Inside the cells, the energy in the molecules is released. Now, you’ll learn how your body cells obtain
energy from the food you eat.
After you eat a meal, your body converts some of the food into glucose, a type of sugar. Respiration is the process by wich cells obtain
energy from glucose. During respiration, cells break down simple food molecules such as sugar and release the energy they
contain. Plant cells, as well as animal cells, respire.
Energy from Respiration
All organisms need energy
to live. The guepard uses
energy to sprint for food.
Although the mushrooms
don’t move, they still need
energy to grow and
reproduce.
Stage
Stage 11 In
In the
the cytoplasm,
cytoplasm, glucose
glucose isis broken
broken down
down
into
smaller
molecules.
Oxygen
is
not
involved
and
into smaller molecules. Oxygen is not involved and aa
small
small amount
amount of
of energy
energy isis released.
released.
Storing and Releasing Energy
During photosynthesis, plants capture the energy from sunlight
and “save” it in the form of carbohydrates, including sugars and
starches. Similarly, when you eat a meal, you add to your
body’s energy savings account. When cells need energy, they
“withdraw” it by breaking down the carbohydrates in the
process of respiration.
Breathing and Respiration
Breathing: moving air in and out of your lungs.
Respiration: this process takes place inside the cells and is
sometimes called cellular respiration.
The two terms are connected: Breathing brings oxygen, which
is usually necessary for cellular respiration.
Like photosynthesis, respiration takes place in two stages.
Stage
Stage 22 In
In the
the mitochondria
mitochondria ,, the
the smaller
smaller molecules
molecules
combine
combine with
with oxygen
oxygen to
to produce
produce water
water and
and carbon
carbon
dioxide.
This
reaction
releases
a
large
amount
dioxide. This reaction releases a large amount of
of
energy.
energy.
The Respiration Equation:
The events of respiration can be summed up by the following chemical equation:
C6H12O6
sugar
+
6 O2
6 CO2
+
6 H2O
oxygen
carbon dioxide
water
+
energy
Notice that the raw materials for respiration are sugar an oxygen. Plants and other
organisms that undergo photosynthesis make their own sugar. The glucose in the cells
of animals and other organisms comes from the food they consume. The oxygen used
in respiration comes from the air or water surrounding the organism.
Photosynthesis and Respiration
Photosynthesis and respiration can be
thought of as opposite pracesses.
Together these two peocesses form a
cycle that keeps the levels of oxygen
and carbon dioxide fairly constant in the
Earth’s atmosphere. As you can see in
this figure , living things use both gases
over and over again.
3. Cell Division
All cells are derived from preexisting cells.
Cell division is the process by wich cells produce new
cells.
3.1. Reasons for cell division
Cell growth
Repair and replacement of damaged cell parts: some
tissues must be repaired often such as the lining of gut,
white blood cells, skin cells with a short lifespan. Other
cells do not divide at all after birth such as muscle and
nerve.
Reproduction of the species.
3.2. Cell Cycle
During a cell’s life cycle there are various different phases.
The Cell Cycle includes two main parts:
Interphase: is the longest part of a cell’s life cycle and
is called “the resting stage” because the cell isn´t
dividing. during interphase. During interphase cell grows,
develops, makes a copy of its DNA, prepares to divide
into two cells and carry on all their normal metabolic
functions.
Cell division: includes Mitosis (nuclear division) and
Cytokinesis (division of the cytoplasm).
3.3 Mitosis
Centromere
Mitosis is the process by which somatic cells divide and
multiply. It results in the production of two daughter cells
from a single parent cell. The two daughter cells are
identical to one another and to the original parent cell. In a
typical animal cell, mitosis can be divided into four
principal stages:
Prophase: The chromatin, diffuse in interphase,
condenses to form double-rod structures called
chromosomes. Each chromosome has duplicated and
now consists of two sister chromatids (the two rods).
Each chromatid in a chromosome is an exact copy of the
other. The two chromatids are held together by a structure
called centromere. At the end of the prophase, the
nuclear envelope breaks down.
Metaphase: The chromosomes align at the equatorial
plate and are held in place by microtubules attached to
the mitotic spindle and to part of the centromere.
Anaphase: The centromere divide. Sister chromatids
separate and move toward the corresponding poles.
Telophase: Daughter chromosomes arrive at the poles
and the microtubules dissapear. The condensed
chromatin expands and the nuclear envelope reappears.
Cytokinesis: The cytoplasm divides, the cell membrane
pinches inward ultimately producing two daughter cells.
Sister
Chromatids