Section 1 : PHOTOSYNTHESIS Part 1

Summary

This educational video script delves into the process of photosynthesis, focusing on its two main phases: light-dependent reactions and light-independent reactions. It explains how plants and certain other organisms convert light energy into chemical energy, producing glucose and oxygen. The script details the role of chloroplasts, thylakoids, and the electron transport chain, highlighting the production of ATP and NADPH in the light-dependent phase. It also touches on cyclic and noncyclic photophosphorylation, emphasizing the importance of these processes for generating energy-rich molecules necessary for plant growth.

Takeaways

• 🌿 Photosynthesis is the process by which green plants, some algae, and certain bacteria convert light energy into chemical energy, producing glucose and oxygen.
• 🔆 The process is divided into two main phases: light-dependent reactions and light-independent reactions (Calvin cycle).
• 🌱 Light-dependent reactions occur in the thylakoid membranes of chloroplasts and involve the production of ATP and NADPH.
• 💧 Photolysis, the splitting of water molecules, provides electrons and protons for the light-dependent reactions and releases oxygen as a byproduct.
• 🔁 Electron transport chains transfer excited electrons through a series of proteins, pumping protons into the thylakoid space to create a concentration gradient.
• 🔋 Chemiosmosis uses the proton gradient to generate ATP by allowing protons to flow back into the stroma through ATP synthase.
• 🌀 Cyclic and non-cyclic photophosphorylation are two types of electron transport processes; cyclic does not produce NADPH or oxygen, while non-cyclic does.
• 📍 The Calvin cycle, occurring in the stroma of chloroplasts, uses ATP and NADPH to fix carbon dioxide into glucose.
• 🌱 Chloroplasts are the organelles in plant cells where photosynthesis takes place, containing thylakoids and stroma.
• 🔬 Photosystems I and II are key components of the light-dependent reactions, with PSII initiating the process by absorbing light and splitting water.

Q & A

What is photosynthesis and how does it relate to cellular respiration?

Photosynthesis is a process where green plants, some algae, and certain bacteria convert light energy into chemical energy by using carbon dioxide and water to produce glucose and oxygen. It is the reverse of cellular respiration, where organisms convert glucose and oxygen into carbon dioxide, water, and energy.

How is light energy converted into chemical energy during photosynthesis?

Light energy is converted into chemical energy through two main phases of photosynthesis: the light-dependent reactions and the light-independent reactions (Calvin cycle). In the light-dependent reactions, light energy excites electrons which are then used to produce ATP and NADPH. These energy-rich molecules are then used in the Calvin cycle to fix carbon dioxide into glucose.

What are the two phases of photosynthesis and what happens in each?

The two phases of photosynthesis are the light-dependent reactions and the light-independent reactions (Calvin cycle). The light-dependent reactions occur in the thylakoid membranes of the chloroplast and involve the production of ATP and NADPH using light energy. The light-independent reactions take place in the stroma of the chloroplast and use ATP and NADPH to convert carbon dioxide into glucose.

What are the roles of chloroplasts in photosynthesis?

Chloroplasts are the organelles in plant cells where photosynthesis takes place. They contain pigments like chlorophyll that absorb light energy and use it to power the light-dependent reactions. The chloroplast has a double membrane structure with thylakoids (stacked as grana) where light-dependent reactions occur, and stroma where light-independent reactions take place.

What are the two types of photosystems involved in photosynthesis and what is their function?

There are two types of photosystems involved in photosynthesis: Photosystem I and Photosystem II. Photosystem II absorbs light at around 680 nanometers and uses it to split water molecules, releasing oxygen and electrons. Photosystem I absorbs light at around 700 nanometers and uses the excited electrons from Photosystem II to produce ATP and NADPH.

How does the splitting of water molecules contribute to photosynthesis?

The splitting of water molecules, also known as photolysis, occurs in the light-dependent reactions of photosynthesis. It provides electrons that are used to generate ATP and NADPH, and it also releases oxygen as a byproduct.

What is the role of ATP and NADPH in the second phase of photosynthesis?

ATP and NADPH, produced in the light-dependent reactions, are used in the light-independent reactions (Calvin cycle) to power the conversion of carbon dioxide into glucose. ATP provides the energy, and NADPH provides the reducing power necessary for this process.

What is chemiosmosis and how does it relate to ATP production in photosynthesis?

Chemiosmosis is the movement of protons (H+) across a membrane, driven by a concentration gradient, which is used to generate ATP. In photosynthesis, a proton gradient is created across the thylakoid membrane during the electron transport chain, and the flow of protons back into the thylakoid space through ATP synthase drives the synthesis of ATP from ADP.

What are the differences between cyclic and noncyclic photophosphorylation?

Cyclic photophosphorylation involves only Photosystem I and results in the production of ATP without the production of NADPH or the release of oxygen. Noncyclic photophosphorylation involves both Photosystems I and II, leads to the production of both ATP and NADPH, and includes the photolysis of water, releasing oxygen as a byproduct.

Why do cells perform cyclic photophosphorylation?

Cells perform cyclic photophosphorylation to generate additional ATP when the demand for ATP is high and the need for NADPH is low. This process does not produce NADPH and is more efficient for ATP production.

Outlines

00:00

🌿 Introduction to Photosynthesis

This paragraph introduces the topic of photosynthesis, explaining it as the process by which green plants produce their own food using carbon dioxide and water in the presence of sunlight. The process is divided into two parts: Part One discusses the light-dependent reactions that occur in chloroplasts, while Part Two, to be covered in a subsequent video, will delve into the light-independent reactions. The paragraph emphasizes the importance of understanding key concepts for exams rather than getting into intricate details. It also mentions that photosynthesis is not exclusive to plants but is also performed by certain algae and bacteria, highlighting the broader scope of this biological process.

05:03

🔬 The Mechanism of Photosynthesis

This section delves into the specifics of photosynthesis, focusing on the light-dependent reactions that take place in the chloroplasts. It describes the structure of chloroplasts, including the thylakoid membranes where the light-dependent reactions occur, and the stroma where the light-independent reactions occur. The paragraph explains the role of photosystems, particularly Photosystem II, in the initial stages of electron transport. It details how light energy is absorbed, leading to the excitation of electrons and the subsequent splitting of water molecules into protons (H+) and oxygen. The paragraph also discusses the production of ATP and NADPH, which are essential for the subsequent phase of photosynthesis, and the process of chemiosmosis that leads to ATP synthesis.

10:05

🔄 Phosphorylation in Photosynthesis

The final paragraph discusses the two types of phosphorylation in photosynthesis: cyclic and noncyclic. It explains that cyclic phosphorylation involves only Photosystem I and does not require water or produce oxygen or NADPH, but it generates additional ATP. Noncyclic phosphorylation, on the other hand, involves both photosystems and includes the splitting of water, leading to the production of oxygen, ATP, and NADPH. The paragraph concludes with a question to test the viewer's understanding of cyclic phosphorylation, highlighting that photoactivated electrons return to Photosystem I after passing through the electron transport chain, which is characteristic of the cyclic process.

Keywords

💡Photosynthesis

Photosynthesis is a biological process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose or other sugars. In the video, it is described as the process where plants make their own food using carbon dioxide and water in the presence of sunlight, releasing oxygen as a byproduct. This process is crucial for life on Earth as it provides the oxygen we breathe and serves as the basis for the food chain.

💡Autotrophs

Autotrophs are organisms that can produce their own food from inorganic substances. In the context of the video, plants are mentioned as autotrophs because they can perform photosynthesis to create glucose from carbon dioxide and water. The video also mentions that not only plants but also some algae and bacteria can carry out photosynthesis, expanding the concept of autotrophs beyond just plants.

💡Light-dependent reactions

These are the first phase of photosynthesis that require light energy to occur. As explained in the video, these reactions take place in the thylakoid membranes of the chloroplasts and involve the production of ATP and NADPH. These energy-rich molecules are essential for the second phase of photosynthesis, where glucose is synthesized.

💡Chloroplasts

Chloroplasts are organelles found in plant cells that conduct photosynthesis. They are described in the video as double membrane structures containing stacks of thylakoids, known as grana, where light-dependent reactions occur. The chloroplast's primary function is to capture light energy from the sun and use it to produce food for the plant.

💡Thylakoids

Thylakoids are membrane-bound compartments within chloroplasts where the light-dependent reactions of photosynthesis take place. The video explains that each 'coin' or thylakoid is part of a stack called a granum, and it is within these structures that the initial reactions of photosynthesis, such as the splitting of water molecules, occur.

💡Stroma

The stroma is the fluid-filled space within the chloroplast where the light-independent reactions, also known as the Calvin cycle, take place. As mentioned in the video, this is where the ATP and NADPH produced in the light-dependent reactions are used to fix carbon dioxide into glucose, which is a key part of understanding the complete process of photosynthesis.

💡Photosystems

Photosystems are protein complexes in the thylakoid membranes that contain pigments, like chlorophyll, which absorb light. The video describes two photosystems, Photosystem I and Photosystem II, which absorb light at different wavelengths and are essential for the electron transport chain during the light-dependent reactions of photosynthesis.

💡Electron transport chain

The electron transport chain is a series of protein complexes in the thylakoid membrane that transfer electrons from one complex to another, creating a flow of protons (H+) across the membrane. As explained in the video, this flow of protons is used to generate ATP through a process called chemiosmosis, which is a critical part of the light-dependent reactions.

💡Chemiosmosis

Chemiosmosis is the process by which a proton gradient across a membrane is used to generate ATP. In the video, it is described as the mechanism by which ATP is synthesized in the thylakoid membrane as protons move from the high concentration inside the thylakoid space to the low concentration outside, passing through ATP synthase.

💡Cyclic and noncyclic photophosphorylation

These terms refer to two different pathways of electron flow during photosynthesis. Noncyclic photophosphorylation, as discussed in the video, involves both photosystems and results in the production of both ATP and NADPH. Cyclic photophosphorylation, on the other hand, only involves Photosystem I and results in the production of ATP without the production of NADPH or the release of oxygen. The video explains that cells may choose between these pathways depending on their energy and reducing power needs.

Highlights

Photosynthesis is a process where green plants make their own food using carbon dioxide and water in the presence of sunlight.

The process of photosynthesis is divided into two phases: light-dependent reactions and light-independent reactions.

Light-dependent reactions occur in the chloroplasts and produce ATP and NADPH.

Light-independent reactions use ATP and NADPH to produce glucose.

Chloroplasts are double membrane structures that capture light energy for photosynthesis.

Thylakoids are the sites of light-dependent reactions within the chloroplasts.

Stroma is the fluid-filled space in chloroplasts where light-independent reactions take place.

Photosystems are pigments that absorb light of different wavelengths, with two types: Photosystem I and Photosystem II.

In phase one, electrons are activated by light and move through an electron transport chain.

Water molecules are split into H+ ions and oxygen during light-dependent reactions.

ATP is produced by chemiosmosis, which uses the H+ gradient created by the electron transport chain.

NADPH is produced when electrons are transferred to NADP+ during light-dependent reactions.

Cyclic and noncyclic photophosphorylation are two types of processes that generate ATP.

Cyclic photophosphorylation only involves Photosystem I and does not produce NADPH or oxygen.

Noncyclic photophosphorylation involves both photosystems and includes the splitting of water, producing oxygen.

Cells choose between cyclic and noncyclic photophosphorylation based on their ATP and NADPH requirements.

The video concludes with a question about cyclic photophosphorylation, highlighting that photoactivated electrons return to Photosystem I.

Transcripts

hello everyone and welcome to the next

video for the same section that we are

discussing and the same subsection which

is biochemistry in the last video we

discussed about cellular respiration in

this video we will be discussing about

the process of photosynthesis and this

uh particular topic will be dealt in two

videos so this is a part one of the

video and another video we will discuss

part two photosynthesis because it's a

pretty big topic okay but as you know we

are just discussing the key concept

whatever you need to remember for the

exam you're not going to go into the

details of

anything okay so coming to

photosynthesis photosynthesis is a

process in which the plants the green

plants make their own food by taking

carbon dioxide and water in the presence

of sunlight they make the food in the

form of glucose and they liberate oxygen

that you breathe in so in this process

you're actually converting light energy

into chemical energy and and you as you

know this is usually done by autot

tropes autot tropes are organisms that

can make their own food like plants but

please remember photosynthesis is also

carried out by some algae and some

bacteria so plants are the not not the

only one who do photosynthesis okay

there are other organisms on this Earth

who do that anyways so the

photosynthesis the whole process can be

divided into two phases phase one are

light dependent reactions the depend on

light okay so this these particular

reactions they take place in organal

called chloroplast we'll discuss that in

a little bit detail after a few slides

and what is the phase one doing the

light dependent reactions they make ATP

and nadph molecules and these ATP and

nadh nadph molecules that you make in

phase one which is the light dependent

reactions you use them in phase two to

make your final product which is glucose

so again phase one light dependent

reaction you make ATP and nadph phase

two light independent reactions you make

use of that ATP and nadph which you made

in Phase One to make the final product

which is glucose now the next thing is

you have to know some components of

chloroplast chloroplast the whole

function of it is to capture the light

energy which is sunlight and to use it

for making uh food for the plant now the

chloroplast is a double membrane

structure you have an outer membrane and

you have an inner membrane inside the

chloroplast you see these stack of these

coins first each coin is called a thilo

covid and together the stack of coins is

called a granum plural is Gran sometimes

you will see the word Grana Grana means

more than one granum okay so each is a

granum together they are the

Grana now there's something else the

fluid fills space here inside the

chloroplast we call that stroma so

please remember that thids

are where your light dependent reaction

takes place and your light independent

reaction takes place in the stroma so

phase one in the piloid phase two in

stroma this is an important concept

please make make sure you know it now

going into the details of phase one so

we the phase one the first part of phase

one is electron

transport so here what happens look what

happens in here so before we go into

that there is something that something

else that you should know in

photosynthesis we talk about something

called a photos system okay so photos

systems are nothing but they contain

pigments that absorb lights of different

wavelength so there are two photosystems

in photosynthesis you have photosystem

one and photos system 2 so photos system

one absorbs light at around 700

nanometers photosystem 2 absorbs light

at around 680

nanometers so here when you talk about

phase one we don't talk about whour

photosystem first one first we talk

about photo system 2 so we start from

photo system 2 here and I will show you

why because there are two types of uh

phosphorilation we'll go to the cyclic

and acyclic in in a bit but right now

let's focus on the electron transport

chain then we'll move on to that concept

also later on okay so here this is a

sunlight and this is your photo system

to the green things so what happens

first the light is absorbed bi your

photos system because they contain

chlorophyll so when light is absorbed

absorbed they they excite the electrons

so when the electrons are excited or

activated look what is happening a water

molecule is splitting into two H+ ions

and half oxygen

molecule okay now so and then what is

happening this this the two H+ ions that

you are making they stay in the thilo

covid space

okay and the oxygen that you're making

is a waste product remember what does

the photosynthesis do it takes carbon

dioxide and it takes water and it makes

oxygen as a product and it also makes

glucose that will be seen in the next

phase not now the final product glucose

you will get not after phase one you'll

get after phase two okay now what

happens

next now the electrons which are

activated they go on moving between one

electron acceptor to the other okay and

then finally so they go on you know from

one electron acceptor to the other

electron acceptor and when they are

doing that when they are doing that the

protons or the H+ are continuously

pumped inside the thilo covid space this

space okay so finally the electrons go

on uh from one electron accept this is

electron transport chain the electron is

transporting from one to the other to

the other to the other and finally they

come to the electron acceptor called

ferrodoxin ferrodoxin you is present in

photosystem one like the photos system

one transfers the electrons to the you

can say it's almost the um the last in

the series here so the ferrodoxin takes

the electron from photosystem one and

then it transfers this electron to a

molecule called

nadp+ okay which along with the proton

which is present here in this space it

makes something called nadph Remember

after phase one we make two components

we make ATP and we make nadph this is

where where you make nadph now it's turn

for you to make ATP okay how do you make

ATP this is done by a process called

chemiosmosis so what is actually

happening look at this

picture so you when I said when that

when you're splitting water you are

continuously having H+ inside the thilo

covid right inside the thilo covid space

so here in the electron transport chain

this H+ is released outside this this

phas so you have H+ here and you have H+

outside too this creates a concentration

gradient so there are more H+ inside the

thilo covid space than it is outside so

what do you think will happen so so

things always move from a region of high

concentration to a region of low

concentration so your H+ will now start

moving from the thilo covid space

outside okay here outside so how do it

move so look at this this is something

this is something which is called an ATP

synthes it's an

enzyme okay so how does the proton or

the H+ moves it moves through these

channels these enzymes so when the H+

moves through this ATP synthes they

start making ATP so from ADP this enzyme

can make ATP by making use of H+ so now

this is how you make ATP and you make

nadph from phase one look this is the

whole process again so here when light

energy entails photosystem 2 the

electron get activated the water

molecule splits up into two uh protons

and half molecule of oxygen this oxygen

is used uh is released as a waste

product this H+ stays here and then this

electron gets transferred from one

electron area to the other when it does

it starts pumping your H+ also outside

okay so you have H+ inside you have H+

outside now this electron gets carried

from photosystem to to photosystem one

and finally it goes on to something

called ferrodoxin which is the final

electron acceptor ferrodoxin then

transfers this electron to

nadp+ with a proton um um ion together

they make something called nadph and the

H+ inside since H+ is more inside the

piloid space so they want to go outside

to a region of low con uh low

concentration they do that with the help

of ATP synthes which is an

enzyme what does it do it it takes the

H+ or the proton from inside the thid

sprays to outside and when this happens

ADP gets transferred to ATP so these are

your products after your first phase

which is nadph and ATP now the second

phase is when you use this ATP and nadph

to make your final product which is

glucose that will be discussed in the

next video before that you have to know

something called the phosphorilation

there's two type one is cyclic and one

is

noncyclic cyclic means that something

which starts from somewhere and it goes

back this is like a cycle in the cyclic

phosphorilation we just make use of

photo system one there is no photo

system two so you have light and then

you know how look how the electron is

being transferred you start from photos

system one and you go back to photos

system one but when you talk about

non-cyclic phosphorilation so what both

the photosystems are involved

okay so basically you start from photos

system 2 which we just discussed and

then you go to photo system one so the

example that we discussed right now is

was of non-cyclic phosphorilation okay

so here please look here carefully in

cyclic only photosystem one is involved

in for noncyclic both are involved in

cyclic water is not required but

noncyclic we just studied we do the

splitting of water which is photolysis

okay in cyclic phosphorilation oxygen is

not involved in or noncyclic we just saw

oxygen is is involved as the waste

product cyclic phosphorilation you don't

make nadph but in non-cyclic we just

made nadph remember and then the last

one is not very important so here why do

the cells have to do cyclic

phosphorilation then just to make

additional ATP why do cells do noncyclic

so that you get get ATP and nadph for

phase two of photosynthesis that's a

purpose so depending upon what the cell

needs they will either go for the cyclic

or they will go for the non-cyclic F

phosphorilation finally we will discuss

one question and we'll end this video so

this question says which of the

following is true about cyclic

phosphorilation first of all let's see

lost electrons from photos system 2 are

replaced by electron from photo system

one we just said that in in the cyclic

one only photo system one is involved so

there is no way you will have photo

system to here so this option is wrong

look at the next option NAD pH and H+

are produced so in cyclic we do not make

nadph it is not synthesized so your

option two is also wrong look at option

D now photolysis of water molecules

releases the electrons blah blah blah

but we know that in cyclic

phosphorilation we don't use water at

all so we also know if you know about

cyclic phosphorilation you know that

option D is also wrong so the only

option which is suitable here is number

c which is photoactivated electrons pass

along the electron transfer chain before

returning to photo system one returning

means it's a cycle this itself will tell

you something is returning back when

something is Cy click something has to

return back okay so your option is

option C that's your correct answer with

this we end this video thank you so much

for

watching