Question
One scientist cultured Cladophora in a suspension of Azotobacter and illuminated the culture by splitting light through a prism. He observed that bacteria accumulated mainly in the region of [NEET (Odisha) 2019]
(a) violet and green light
(b) indigo and green light
(c) orange and yellow light
(d) blue and red light
Answer/Explanation
Ans. (d)
Engelmann used a prism to split light into its spectral components and then illuminated a green alga, Clodophora placed in a suspension of aerobic bacteria (Azotobacter). The bacteria were used to detect the sites of oxygen evolution.
He observed that bacteria mainly accumulated in the region of blue and red light of the split spectrum, thus giving the first action spectrum of photosynthesis.
Question
In a chloroplast the highest number of protons are found in [NEET 2016, Phase I]
(a) Iumen of thylakoids
(b) inter membrane space
(c) antennae complex
(d) stroma
Answer/Explanation
Ans. (a)
Proton concentration is higher in the lumen of thylakoid due to photolysis of water, $\mathrm{H}^{+}$pumping and NADP reductase activity which occurs in stroma of the chloroplast.
Question
Of the total incident solar radiation the proportion of PAR is [CBSE AIPMT 2011]
(a) about $60 \%$
(b) less than $50 \%$
(c) more than $80 \%$
(d) about $70 \%$
Answer/Explanation
Ans. (b)
PAR (Photosynthetically Active Radiation) designates the spectral range of solar radiation from 400-700 $\mathrm{nm}$ that photosynthetic organisms are able to use in the process of photosynthesis. Of the total incident solar radiation the proportion of PAR is less than $50 \%$.
Question
Stroma in the chloroplasts of higher plants contains [CBSE AIPMT 2009]
(a) light-independent reaction enzymes
(b) light-dependent reaction enzymes
(c) ribosomes
(d) chlorophyll
Answer/Explanation
Ans. (a)
In higher plants, enzymes for light independent reactions (dark reactions) are present in the stroma of chloroplasts. Light dependent reaction occurs in grana of chloroplast.
Ribosomes are necessary for protein synthesis. Chlorophyll is green photosynthetic pigment found in chloroplasts.
Question
Carbohydrates are commonly found as starch in plant storage organs. Which of the following five properties of starch $(\mathrm{A}-\mathrm{E})$ make it useful as a storage material?
A. easily translocated
B. chemically non-reactive
C. easily digested by animals
D. osmotically inactive
E. synthesised during photosynthesis
The useful properties are [CBSE AIPMT 2008]
(a) $B$ and $C$
(b) $B$ and $D$
(c) A, $C$ and $E$
(d) A and $E$
Answer/Explanation
Ans. (c)
Option (c) is correct. As starch is a high
molecular weight polymer of D-glucose in $\alpha \mapsto 4$ linkage. It is synthesised in chloroplasts as one of the stable end products of photosynthesis. It is most abundant and common storage polysaccharide in plants hence, most staple food for man and herbivores.
It is a mixture of two types of glucose homopolysaccharide viz, amylose and amylopectin. During day time the starch synthesis in chloroplast is coordinated with sucrose synthesis in cytosol. Typically about $90 \%$ of total solute carried in phloem is the carbohydrate sucrose, a disaccharide.
This is relatively inactive and highly soluble sugar playing little direct role in metabolism and so, making an ideal transport sugar.
Question
Chlorophyll in chloroplasts is located in [CBSE AIPMT 2004]
(a) outer membrane
(b) inner membrane
(c) thylakoids
(d) stroma
Answer/Explanation
Ans. (c)
The thylakoids of chloroplast are flattened vesicles arranged as a membranous network within the stroma. $50 \%$ of chloroplast proteins and various components involved (namely chlorophyll, carotenoids and plastoquinone) in photosynthesis are present in thylakoid membranes.
Question
Which fractions of the visible spectrum of solar radiations are primarily absorbed by carotenoids of the higher plants? [CBSE AIPMT 2003]
(a) Violet and blue
(b) Blue and green
(c) Green and red
(d) Red and violet
Answer/Explanation
Ans. (a)
Carotenoids are a group of yellow, red and orange pigments which function as accessory pigments and protect chlorophyll molecules from destruction by intensive light rays. Carotenoids have three absorption peaks in the blue-violet range of the spectrum.
Question
Which element is located at the centre of the porphyrin ring in chlorophyll? [CBSE AIPMT 2003]
(a) Manganese
(b) Calcium
(c) Magnesium
(d) Potassium
Answer/Explanation
Ans. (c)
Magnesium is at the centre of the porphyrin ring in chlorophyll. The general structure of chlorophyll was elucidated by Hand Fischer in 1940.
Question
Stomata of CAM plants [CBSE AIPMT 2003]
(a) open during the night and close during the day
(b) never open
(c) are always open
(d) open during the day and close at night
Answer/Explanation
Ans. (a)
CAM (Crassulacean Acid Metabolism) plants open stomata only at night (when temperature is low and humidity is high) to cause lesser loss of water (e.g.
Agave, Opuntia, etc.). So, CAM photosynthesis is a carbon fixation pathway that evolved in some plants as an adaptation to arid condition.
Question
The first step of photosynthesis is [CBSE AIPMT 2000]
(a) excitation of electron of chlorophyll by a photon of light
(b) formation of ATP
(c) attachment of $\mathrm{CO}_2$ to 5 carbon sugar
(d) ionisation of water
Answer/Explanation
Ans. (a)
The entire process of photosynthesis is driven by light energy coming from the sun. This energy is first captured by chlorophyll molecules and later on utilised for the synthesis of ATP (chemical energy) molecules which are later utilised in the dark reaction, i.e., Calvin cycle.
Question
Chlorophyll-a molecule at its carbon atom 3 of the pyrrole ring-ll has one of the following [CBSE AIPMT 1996]
(a) aldehyde group
(b) methyl group
(c) carboxyl group
(d) magnesium
Answer/Explanation
Ans. (a)
Chlorophyll has a tetrapyrrole porphyrin head and a long chain alcohol called phytol tail. Each pyrrole is a 5 member ring with one nitrogen and four carbon. A non-ionic $\mathrm{Mg}$ atom lies in the centre of porphyrin, attached to nitrogen atoms of pyrrole rings. Chlorophyll-a has methyl group at carbon 3 of pyrrole ring and chlorophyll-b has formyl (aldehyde) group attached to this atom.
Question
Pigment acting as a reaction centre during photosynthesis is [CBSE AIPMT 1994]
(a) carotene
(b) phytochrome
(c) $P_{700}$
(d) cytochrome
Answer/Explanation
Ans. (c)
Photosynthetic pigment molecules (e.g. $P_{700}, P_{890}$ Jare able to convert light energy into chemical energy. These pigment molecules which together forms the photosynthetic units, possess photocentres (reaction centre $=$ trap centre) surrounded by harvesting molecules differentiated into core molecules and antenna molecules.
Question
Nine-tenth of all photosynthesis of world ( $85-90 \%)$ is carried out by [CBSE AIPMT 1994]
(a) large trees with millions of branches and leaves
(b) algae of the ocean
(c) chlorophyll containing ferns of the forest
(d) scientists in the laboratories
Answer/Explanation
Ans. (b)
$90 \%$ of total photosynthesis is carried out by aquatic plants, chiefly algae $(80 \%$ in oceans and $10 \%$ in freshwater). $10 \%$ of total photosynthesis is performed by land plants.
Question
Maximum solar energy is trapped by [CBSE AIPMT 1993]
(a) planting trees
(b) cultivating crops
(c) growing algae in tanks
(d) growing grasses
Answer/Explanation
Ans. (d)
Maximum solar energy is trapped by growing grasses, as they have the largest surface area for absorption. Limited number of algal individual are growing in tank so, they absorb limited amount of light.
Question
Chlorophyll-a occurs in [CBSE AIPMT 1992]
(a)all photosynthetic autotrophs
(b) in all higher plants
(c) all oxygen liberating autotrophs
(d) all plants except fungi
Answer/Explanation
Ans. (b)
Chlorophyll-a $\left(\mathrm{C}_{55} \mathrm{H}_{72} \mathrm{O}_5 \mathrm{~N}_4 \mathrm{Mg}\right)$ is a bluish green pigment, it is the primary photosynthetic pigment or universal photosynthetic pigment that occurs in all plants except photoautotrophic bacteria, i.e. found in all oxygenic photoautotrophs.
Question
Photosynthetic pigments found in the chloroplasts occur in [CBSE AIPMT 1991]
(a) thylakoid membranes
(b) plastoglobules
(c) matrix
(d) chloroplast envelope
Answer/Explanation
Ans. (a)
Photosynthetic pigments are those pigments which occur on photosynthetic thylakoids of chloroplasts and absorb light energy for the purpose of photosynthesis. These are mainly of two types-chlorophylls and carotenoids.
Question
The size of chlorophyll molecule is [CBSE AIPMT 1988]
(a) head $15 \times 15 \AA$, tail $25 \AA$
(b) head $20 \times 20 \AA$, tail $25 \AA$
(c) head $15 \times 15 \AA$, tail $20 \AA$
(d) head $10 \times 12 \AA$, tail $25 \AA$
Answer/Explanation
Ans. (c)
A chlorophyll molecule consists of two parts, the porphyrin ring (head) $15 \times 15 \AA$ and a phytol tail (20 Â).