Cell membranes

Cell membranes are thin [four to ten nanometers thick] and fluid films that serve as the outer border of a cell or a cell organelle, which is an internal compartment of the cell. Cell membranes or compartmental membranes are usually differentially permeable. This means that it only encourages some ions molecules to get in while preventing others. Cell membranes are the principal barrier between a cell and its surroundings. Substances enter and exit the cell via the layer. Movement through the cell membrane, on the other hand, is restricted to chemical and ion molecules such as water and oxygen. Through diffusion, oxygen, water, and carbon dioxide can cross the cell membrane. The differential permeability of the cell membrane to water is known as osmosis.
The cell membrane keeps toxic substances at bay from the cell. The cell membrane also has receptors that permit molecules such as ions, waste and nutrients pass into and out of the cell and its organelles, selectively. Thirdly, cell membranes separate vital processes that go on inside the organelles that may be incompatible in the instance that they did not exist for organelles.
Membranes enclose compartments with cells. Different compartments within the cell perform given roles and have diverse compositions. Instances of such chambers entail chloroplasts, organelles, and mitochondria. The process of their formulation is known as compartmentalization.
Structure of membranes
On its outer boundary lies the plasma membrane. There are some more membranes enclosing compartments in the inside of cells known as cell organelles. Proteins on the plasma membrane are responsible for water and ions transportation into and out of the cell.
There are some other proteins on the layer that enhances diffusion of ions in and out of the cell. Some other proteins bind to molecules on one side and transport them to the other. In some other cases, some proteins transport molecules in opposite directions seamlessly.
The process by which transportation occurs from plasma membrane is known as endocytosis. Charged, non-polar molecules that are small can pass through the cell membrane, which is usually charges. On the other hand, larger ion molecules, which are typically charged may not. Mostly, this is because charged molecules repel others that aren’t.

Figure 1: the membrane of the cell allows for selective permeability of water and ion-molecule into and out of the cell.
Via diffusion, substances move from higher areas of concentration to others that aren’t as highly concentrated. Via simple diffusion, ions are transported through openings on the membrane or other spaces between molecules without interacting with the membrane’s carrier proteins whatsoever.
Osmosis is the process by which solvent moves across a membrane to another solution with a higher solute concentration. Osmotic pressure is required to maintain a state of equilibrium across two solutions without the occurrence of osmosis.
Active transport requires a lot of energy since the movement of molecules is against a concentration gradient. Proteins carriers, as well, are expected to move molecules across a semi-permeable membrane from zones where they are lowly concentrated to others where they are highly concentrated. This is the implication of “contrary to their concentration gradient.”
Question 2
Glycolysis details how glucose is broken down to produce energy. Glycolysis happens in all living things, and energy production is spent up during functioning of cells, known as cell metabolism. Typically, during glycolysis, two pyruvates, two ATP, and two NADH molecules are produced. ATP (adenosine triphosphate) is the form in which energy is created. The production process happens in two distinct phases. Coenzymes are molecules that play a crucial role in enzyme activities by binding to the later. Usually, enzyme speeds up cellular reactions. Whereas they coenzymes cannot, they aid enzymes to do so.
Glucose (with six carbons) transforms into two pyruvates (sugars with three carbons) through several enzyme reactions. Soon after glycolysis, acetyl-Coenzyme A is formed within the cell’s mitochondrion, after reaction of coenzyme A with pyruvic acid from the pyruvate molecules. This first phase needs energy in the forms of NADH molecules. The second stage is defined by formation of pyruvates and the last productions two adenosine triphosphate molecules.

Further, in the Krebs cycle, which is linked to glycolysis, more energy is produced to meet cell metabolism needs in the form of ATP. In this sequence, oxygen is spent up further with further reactions that produce more ATP. Oxygen here is gotten from NADH to produce more ATPs.
Figure 2: During cells respiration, glycolysis oxidizes glucose molecules. Soon follows the Krebs cycle, alongside phosphorylation that produces ATP
It’s worth mentioning that energy generated within this process is spent to repair tissues that may be worn out and to perform other crucial functions of the cell.
Structure of proteins
Proteins bind to other molecules and ions. Their ability to play characters of signal receptors, catalysts alongside others largely depends on their binding ability. For instance, antibodies enjoin bacteria and viruses in readiness for destruction. Coupling in some cases is loose and short-lived whereas it is tight in some others. Specific proteins bind to specific molecules from the many there may be. The particle or ion to which a protein link is known as a ligand. A proteins binding site is usually a cavity on this surface formed from an arrangement of amino acids;
Figure 3

Moreover, PH and temperature are factors that influence the activity of enzymes and eventually, metabolism in cells. Cofactors molecules once bind to proteins influence they’re active, positively. Regulators either boost or bring down enzyme activity. Activators are regulators that increase it while inhibitors, on the other hand, reduce the enzyme activity.
Allosteric regulation occurs when an inhibitor or activator binds to an enzyme in an allosteric site different from the active site.
Structure of ATP
Adenosine triphosphate is a nucleotide. It has three phosphate groups attached to a five-carbon sugar attached to a nitrogen base. ATP is unstable due to 3 negative charges against this phosphates groups. This instability is because such negative charges repel each other. The ATP is so adamant to lose the phosphate group.

Figure 4: structure of ATP

In reaction coupling in cells, involves a molecule with a phosphate group, and may have the release of energy soon after ATP is converted to ADP within cell metabolism.
Question 3
Electron transport chain located in the chloroplast and mitochondria is the backbone of photosynthesis and respiration processes. Electron transport chain is also referred to as the light reaction since it is a light-driven reaction. The electron transport chains are organized with the photosystems in the thylakoid membranes enabling pumping of hydrogen via that layer. The electron transport chain is effective to produce a reducing power as well as oxygen from water due to light energy. NADH passes hydrogen ions and heat to the Adenosine triphosphate synthetase. The energy from the two combines to forms ATP. Oxygen which is the final atom acceptor together with the electron transport chain is subject to the proton angle found in the inner parts of the membrane of the mitochondria. The protons take over the mechanism enabling the P to be attached to ADP to form ATP. The electron transport is essential for both photosynthesis and respiration processes it gives rise to two vital products that are NADPH2 which a reducing agent and ATP which is an energy-rich compound. The two products of electron transport chain are used in the dark stage of photosynthesis.
Chlorophyll is a collection of green pigments located in the chloroplast of plants. Chlorophyll contains porphyrin ring which allows free movement of electrons. ATP synthase is an enzyme that generates energy storage molecules called ATP that is adenosine triphosphate. ATP synthase is in the inner membranes of the mitochondria. ATP synthase is made of two regions which include; FO and F1. F0 results to the rotation of F1. Also, F0region is made of C shaped rings. F1has a portion which is water soluble used the hydrolysis of ATP.
The two regions of the ATP synthase create a pathway for the movement of the protons across the membrane.
Four events take place in the electron transport chains of the chloroplast and the mitochondria. The light energy is absorbed by the electrons found in the chlorophyll breaking down water into hydrogen, oxygen, and electrons. Secondly, hydrogen ions are pumped into thylakoid space by the electron transport chains. Thirdly, NADP+ combines with the hydrogen ions to form NADPH. Finally, the hydrogen ions in the thylakoid space are passed through the ATP synthase the membranes of the thylakoid making it rotate and generate energy-rich compound called adenosine triphosphate.
The overall function of electron transport chain is regenerate NAD+ and FAD with free energy that is used to produce ATP. Another role of electron transport chain is to reduce oxygen into water. ATP is used as the source of energy during the process of photosynthesis in plants.

The electron transport chains

Figure 5
Question 4
A chloroplast is an organelle found in the plant cell that contains chlorophyll which is the green coloring matter of a plant. The chloroplast is where food making process in plants known as photosynthesis takes place. Chloroplast converts sunlight into chemical energy. Chloroplasts can be in the cells of the mesophyll in the plant’s leaves. The chloroplast contains membranes, which are the inner and the outer membranes with space at the middle. Inside the chloroplasts, there are thylakoids compounds known as the grana or the stroma which is the dense fluid found inside the chloroplast. The thylakoids in the chloroplast, have chlorophyll which is essential for plants to undergo photosynthesis. The space occupied by the chlorophyll is known as thylakoid space.
Structure of the chloroplast

Figure 6
The mechanism of photosynthesis takes place into phases. The two-phase are light and dark stage reaction.
Light reaction- the reaction occurs in the presence of light, in the region of chloroplast known as the grana. The reaction is photochemical as it cannot take place without light. In this reaction, light energy is received by the colors in the chloroplast known as the chlorophyll. In the light reaction phase, the light energy is received by the electrons found in the chlorophyll breaking down water into hydrogen, oxygen, and electrons. Hydrogen ions are pumped into thylakoid space by the electron transport chains. NADP+ combines with the hydrogen ions to form NADPH. Finally, hydrogen ions in the thylakoid space are passed through the ATP synthase the membranes of the thylakoid making it rotate and generate energy-rich compound called adenosine triphosphate.
Dark reaction- the reaction takes place both the presence and absence of light. The reaction occurs in the stroma of the chloroplast. Also, the reaction is a thermos chemical reaction. In this reaction, there is no absorption of light. Carbon IV oxide is used in this reaction whereby it is used in the synthesis of sugars. The end products of the light stage reaction; ATP and NADPH2 are used in the dark stage.
comparison of C-3 plants and C-4 plants
C-3 plants C-4plants
The leaves have large airspaces that are bordered by spongy mesophyll cells which are loosely arranged. Have thinner leaves with closer arrangement of the vascular bundles. The airspaces are small
The opening of the stoma takes place during and the closure during the night. The opening of the stoma takes place during and the closure during the night.
They are found in temperate areas. They are found in tropical or semi-tropical areas.
Have C-3 photosynthesis They have C-4 photosynthesis

The leaves have large airspaces that are bordered by spongy mesophyll cells which are loosely arranged.
Have thinner leaves with a closer arrangement of the vascular bundles. The airspaces are small
The opening of the stoma takes place during and the closure during the night.
The stomata open during the day and close and night.
They are found in temperate areas.
They are found in tropical or semi-tropical areas.
Have C-3 photosynthesis
They have C-4 photosynthesis
Adaptations of C-4 plants to their habitats
They have thinner to reduce water loss.
They have small airspaces.
They minimize the capturing of carbon IV oxide during the process of photosynthesis to components that are usable.
They convert carbon IV oxide to oxalate which is a four-carbon acid.
Photosynthetic carbon reaction.
Photosynthetic carbon reduction is a process in which the synthesis of sugar from the carbon IV oxide takes place. The process occurs in the dark stage where carbon IV oxide combines with 5-carbon sugars, 1,5-biphosphate, and ribulose to form an unstable six-carbon sugar. The sugar component the breaks down as shown in the diagram below;
Photosynthetic carbon reaction cycle

Works cited
Hay, Elizabeth D., ed. Cell biology of extracellular matrix. Springer Science & Business Media, 2013.
Skulachev, Vladimir P. Membrane bioenergetics. Springer Science & Business Media, 2013.
Tcherkez, G., Gauthier, P., Buckley, T.N., Busch, F.A., Barbour, M.M., Bruhn, D., Heskel, M.A., Gong, X.Y., Crous, K.Y., Griffin, K. and Way, D., 2017. Leaf day respiration: low CO2 flux but high significance for metabolism and carbon balance. New Phytologist.
Yamori, W. and Shikanai, T., 2016. Physiological functions of cyclic electron transport around photosystem I in sustaining photosynthesis and plant growth. Annual review of plant biology, 67, pp.81-106.
Yamori, Wataru, Kouki Hikosaka, and Danielle A. Way. “Temperature response of photosynthesis in C3, C4, and CAM plants: temperature acclimation and temperature adaptation.” Photosynthesis research 119, no. 1-2 (2014): 101-117.