Respiration always does not require $\mathrm{O}_2$. There are organisms which respire even in absence of $\mathrm{O}_2$ through anaerobic respiration.
The first cells of earth i.e., chemosynthetic bacteria are the primitive organisms of early life on earth. Obtained energy by breaking down inorganic molecules like $\mathrm{H}_2 \mathrm{~S}, \mathrm{NO}_2^{-}$, etc.
e.g., chemosynthesis occured in sulphur bacteria in the following way
$$12 \mathrm{H}_2 \mathrm{S}+6 \mathrm{CO}_2 \rightarrow \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{H}_2 \mathrm{O}+12 \mathrm{S} \downarrow$$
There are basically two kinds of muscle fibers
(i) Red muscles
(ii) White muscles
Red muscles work for a longer time continuously because
(i) These muscle fibres are dark red which is due to the presence of red haemoprotein called myoglobin. Myoglobin binds and stores oxygen as oxymyoglobin in the red fibres. Oxymyoglobin releases oxygen for utilisation during muscle contraction.
(ii) Mitochondria are more in number, hence they work for long periods of time.
(iii) Red muscles have less sarcoplasmic reticulum.
(iv) They carry out considerable aerobic oxidation without accumulating much lactic acid. Thus, red muscle fibres can contract for a longer period without fatigue.
(v) These muscle fibres have slow rate of contraction for long periods. e.g., extensor muscles of the human back.
The energy yield in terms of ATP is higher in aerobic respiration than during anaerobic respiration is as given
| Aerobic Respiration | Anaerobic Respiration |
|---|---|
| In aerobic respiration, there is complete oxidation of substrate molecules producing ATP molecules. | In anaerobic respiration there is incomplete oxidation of substrate molecules so the ATP produced are less in number. |
| Aerobic respiration of glucose produces 36 ATP molecules $+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2$. | Anaerobic respiration of glucose, when occurs in yeast, produces 2 ATP molecules+ ethy lalcohol $+\mathrm{CO}_2$. |
RuBP carboxylase, PEPcase, pyruvate dehydrogenase, ATPase, cytochrome oxidase, hexokinase, lactate dehydrogenase. Select/choose enzymes from the list above which are involved in
(a) Photosynthesis (b) Respiration (c) Both in photosynthesis and respiration
RuBP Carboxylase This is a part of dark reaction of photosynthesis. It catalyses the fixing of $\mathrm{CO}_2$ in $\mathrm{C}_3$ cycle.
PEPcase This is a part of photosynthesis of $\mathrm{C}_4$ plants. It catalyses the reaction of fixing of $\mathrm{CO}_2$ to form first stable product oxaloacetate. 4 carbon compound.
Pyruvate dehydrogenase It is involved in aerobic respiration and catalyses the reaction of formation of acetyl Co-A from pyruvic acid. It requires the participation of NAD and Co-enzyme-A.
Pyruvic acid $+\mathrm{Co}-\mathrm{A}+\mathrm{NAD}^{+} \xrightarrow[\text { Pyruvate dehydrogenase }]{\mathrm{Mg}^{2+}}$ Acetyl $\mathrm{Co}-\mathrm{A}+\mathrm{CO}_2+\mathrm{NADH}+\mathrm{H}^{+}$
ATPase It is a part of both respiration and photosynthesis. Both these processes uses electron transport chain and associated proton pump and ATP synthase as a key part of process. ETC uses the energy to pump hydrogen ions across a membrane.
The protons flows back through ATP synthase, driving the production of ATP.
Cytochrome Oxidase This is involved in both respiration and photosynthesis. It is an electron carrier in the electron transport chain. Hexokinase This enzyme is also involved in, respiration. In glycolysis, it catalyses the first reaction, i.e., formation of glucose -6- phosphate from glucose molecule. It uses one ATP molecule which transfers $\mathrm{PO}_4$ group to glucose molecules.
Lactate Dehydrogenase
This enzyme is involved in anaerobic respiration in bacteria Lactobacillus. Pyruvic acid formed at the end of glycolysis is converted to lactic acid by homo-fermentative lactic acid bacteria. Hydrogen from NADH molecule is transferred to pyruvate is transferred to pyruvate molecule lactic acid molecule leading formation of acid.
$\underset{\substack{\text { Pyruvic acid }}}{\mathrm{CH}_3 \mathrm{COCOOH}}+$ NADH. $\underset{\text { Dehydrogenase }}{\stackrel{\text { Lactate }}{\longrightarrow}} \underset{\text { Lactic acid }}{\mathrm{C}_3 \mathrm{H}_6 \mathrm{O}_3}+$ NAD
The old tree trunk is covered by dead woody tissue called cork. The epidermal layers of such tree get ruptured and outer cortical cells are loosely arranged. These structures are called as lenticels.
These are the sites of gases exchange and transpiration.
