Biology Reviewer

Photosynthesis

Photosynthesis - is a process that uses light to make food energy flow

through ecosystem.
Energy flow through ecosystems begins when plant capture sunlight and
convert it to chemical energy.
Photosynthesis: Metabolic pathway that uses light energy to turn
carbon dioxide (CO2) and water (H2O) into carbohydrates (sugar).

Two Stages Of Photosynthesis

Light Dependent Reaction - happens inside the thylakoid.
Light Independent Reaction- happens in the Stroma.
Chloroplast - organelle where photosynthesis happen.

Stroma- where light independent reaction happens.

Thylakoid- where light dependent reaction happens

Why light dependent reaction?

Because in the two stages this is the part where it needs energy from the
sun. During this reaction the thylakoid will absorb the light from the
sun to spit the water into hydrogen into oxygen and during this
entire process oxygen is released to the atmosphere and
hydrogen is used to make ATP and ADP, which will then be used
for the next reaction which is the light independent reaction or
Calvin.
Light Dependent happens inside the thylakoid and inside the thylakoid
there are thylakoid membrane and inside the thylakoid the space inside is
called lumen.

In the thylakoid membrane there is something called the photosystem 2

and photosystem 1. So what happens the thylakoid membranes absorb
the energy from the sun. So in the photosystem 2 to energize the electron
and if the electron is energize it will move to the photosystem 1 with the
help of the electron transport chain. and while the electron is moving this
is the part where the water is split. if the electron arrives at photosystem
1 it has no more energy because it has been used to split the water so
that’s why thylakoid will take light energy again to energize the electron..
If the photosystem 1 is completed the electron will be used to react with
ADP to make an ATP and then the hydrogen that is formed in the lumen
will be used by ATP synthase to convert the ADP to ATP.
Remember that ATP is the energy currency of the cell, which means. it is
the energy that is used by cell to work properly. The ADP and ATP will
used by light independent reaction to make the glucose.
Hydrogen is formed in the lumen.

A pigment is a light absorbing molecule that absorb only

specific wavelengths of light, while reflecting others. There are many
different types of pigments in nature, but chlorophyll is unique in its ability
to enable plants to absorb the energy they need to manufacture food.

What is Chlorophyll?
a green pigment found in plants, algae and phytoplankton. This molecule
is used in photosynthesis as a photoreceptor. It makes plants and algae
appear green because it reflects green wavelengths found in sunlight,
while absorbing all other colors.

6 different types of chlorophyll that have been identified.

The different forms are A, B, C, D, E, and F each reflect slightly different

ranges of green wavelengths.

Chlorophyll A
Is the primary molecule responsible for photosynthesis.
It is found in every single photosynthesizing organism, from land plants to
algae and cyanobacteria. The additional chlorophyll forms are accessory
pigments, and are associated with different groups of plants and algae
and play a role in their taxonomic confusion. These other chlorophyll still
absorb sunlight, and thus assist in photosynthesis. As accessory pigments,
they transfer any energy that they absorb to the primary chlorophyll A
instead of directly participating in the process.
Chlorophyll B is mainly found in land plants, aquatic plants and green
algae. In most of these organisms, the ratio of chlorophyll A to chlorophyll
B is 3:1. Due to the presence of this molecule, some organizations will
group the green algae into the Plant Kingdom.
Chlorophyll C is found in red algae, brown algae, and dinoflagellates.
This has lead to their classification under the Kingdom Chromista.
Chlorophyll D is a minor pigment found in some red algae,
Chlorophyll E has been found in yellow-green algae.
Chlorophyll F was recently discovered in some cyanobacteria near
Australia. Each of these accessory pigments will strongly absorb different
wavelengths, so their presence makes photosynthesis more efficient.

Other Pigments
 carotenoids
 phycobilin (biliproteins)
 anthocyanins.
These accessory pigments are responsible for other organism
colors, such as yellow, red, blue and brown. Like chlorophylls B, C, D, E
and F, these molecules improve light energy absorption, but they are not
a primary part of photosynthesis.

Carotenoids absorbs violet and blue-green light and reflect yellow,

orange and/or red light. It help capture light but they also have an
important role of getting rid of excess light energy. When a leaf is
exposed to full sun, it receives a huge amount of energy; if that energy is
not handled properly, it can damage the photosynthetic machinery.
Carotenoids in chloroplasts help absorb the excess energy and dissipate it
as heat. This pigment is also important for the dispersal of plant seeds
because it attract insects. Example of carotenoids are carotene found in
carrots, lutein (xanthophyll) yellow pigment found in fruits and
vegetables, and lycopene found in the red pigment of tomatoes.
There are two phycobilin found in phytoplankton:
phycoerythrin and phycocyanin. Phycocyanin reflects blue light and is
responsible for cyanobacteria’s common name – blue-green algae. It
absorbs extra orange and red light. Phycoerythrin reflects red light, and
can be found in red algae and cyanobacteria. It absorbs dim and blue-
green light.
Some algae will appear green despite the presence of these
accessory pigments. Just as in plants, the chlorophyll in algae has a
stronger relative absorption than the other molecules. Like a dominant
trait, the more intense, reflected green wavelengths can mask the other,
less-reflected colors. In green algae, chlorophyll is also found at a higher
concentration relative to accessory pigments. When the accessory
pigments are more concentrated such as in red algae, brown algae and
cyanobacteria, the other colors can be seen.

Anthocyanins are blue, red, or purple pigments found in plants,

especially flowers, fruits, and tubers. In acidic condition, anthocyanin
appears as red pigment while blue pigment anthocyanin exists in alkaline
conditions. Anthocyanins found in plants have a wide range of usage.
Blue, red and purple colored pigments extracted from flowers, fruits, and
vegetables are traditionally used as dye and food colorant. Besides being
used as natural colorants, some of the anthocyanin-rich flowers and fruits
have been used as medicine to treat various diseases. Plant anthocyanins
possess antidiabetic, anticancer, anti-inflammatory, antimicrobial, and
anti microbial and anti-obesity effects, as well as prevention of
cardiovascular diseases. With this, anthocyanins extracted from edible
plants are potential pharmaceutical ingredients.

PHOTOSYNTHESI Process by which photosynthetic organisms like

S plants transform light energy into chemical
energy.
PIGMENT Colored substance produced by plant that
absorb light rays from the visible region of the
electromagnetic spectrum
PHOTORECEPTOR A molecule that traps light energy
CHLOROPLAST Organelles found in plant cells that conduct
photosynthesis
THYLAKOIDS Are membrane-bound compartments inside the
chloroplasts and cyanobacteria where light
absorption happens
CHLOROPHYL A Primary pigment in plant; absorbs yellow and
blue light; reflects green light
ACCESSORY Are light-absorbing compounds found in
PIGMENTS photosynthetic organisms that work in
conjunction with chlorophyll a.
CAROTENOIDS Accessory pigment; yellow to red pigments found in
almost every leaf that absorb some of the green
light that chlorophyll cant
CAROTENE Accessory pigment; are orange, yellow and red
pigments found largely in fruits, vegetables and
dark green leafy vegetables
BETA CAROTENE Accessory pigment; carotene found in carrots
LYCOPENE Accessory pigment; red pigment found in red fruit
and tomatoes
XANTOPHYLL Accessory pigment; brown or yellow colored
oxygenated hydrocarbons; found in saffron
PHYCOBILINS Accessory pigment found in cyanobacteria;
absorb green to red wavelength of light
PHYCOERYTHRIN Accessory pigment found in red algae and
cyanobacteria; absorb dim and blue-green light
PHYCOCYANIN Accessory pigment found in red algae and
cyanobacteria; absorb extra orange and red light
ANTHOCYANIN Accessory pigment; reflect red, blue and violet light;
considered as an excellent antioxidant
LIGHT ENERGY Energy coming from the sun; the visible light in the
electromagnetic spectrum;
ABSORPTION Set of wavelengths absorbed by a pigment
SPECTRUM
PAPER useful technique in the separation and identification
CHROMATOGRAP of different plant pigments.
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