Succulent plants grow in dry and xeric conditions so, they have to shut down the stomata during day time, to prevent water loss through transpiration. So and the gaseous exchange does not take place. Thus plants have developed the mechanism to fix $\mathrm{CO}_2$ during night in the form of malic acid, which is a 4 carbon compound and store $\mathrm{CO}_2$, release it during day, inside the photosynthetic cells.

Accessory pigments are also photosynthetic pigments. These are chlorophyll-b, xanthophyll and carotenoids. These are not directly involved in emission of excited electrons, but they help in harvesting solar radiation and pass it on to chlorophyll-a. This pigment itself absorbs maximum radiation at blue and red region. So, Chlorophylla is the chief pigment of photosynthesis and others (i.e., chlorophyll-b, xanthophyll and carotinoion) are accessory pegment.

$\mathrm{CO}_2$ is reduced through various biochemical reactions to produce $\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6$ (glucose) which does not need light. But they depend on the products formed during light reactions, i.e., $\mathrm{NADPH}_2$ and ATP.

Photosynthesis and respiration are related, as in both mechanisms, the plants gain energy. In photosynthesis, plants gain energy from solar radiations whereas, in respiration, they break down glucose molecule to get energy in the form of ATP molecules. They are releted also because they are dependent on each other. The product of photosynthesis i.e., glucose (food) is utilised in respiration to yield energy (ATP). Which doing so, it releases many other simple molecules $\left(\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}\right)$ which are utilised in photosynthesis to produce more sugers.

The plant in given conditions can not carry out photosynthesis. Light is must for any green plant to make its own food. The plant should be watered properly for its survival.