Photosynthesis

Question 1

How does energy enter an organism?

Answer 1

• It depends on its type of nutrition
• in plants energy and light is absorbed by chlorophyll and then transferred into the chemical energy of the molecules formed during photosynthesis
• these molecules are used by the plant to produce ATP during respiration
• non-photosynthetic organisms feed on the molecules produced by plants and then also use them to make ATP during respiration

Question 2

How does photosynthesis support the existence of almost every organism?

Answer 2

• the energy we rely on, whether it comes from food when we respite or from the wood, coal, oil and gas that we burn in our homes, has been captured by photosynthesis from sunlight
• photosynthesis likewise produces the oxygen we breath by releasing it from water molecules

Question 3

What is the site of photosynthesis?

Answer 3

• the leaf is the main photosynthetic structure in eukaryotic plants
• chloroplasts are the cellular organelles within the leaf where photosynthesis takes place

Question 4

What are the adoptions of leaves?

Answer 4

• a large surface area that absorbs as much sunlight as possible
• an arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of one leaf by another
• thin, as most light is absorbed in the first few micrometres of the leaf and the diffusion distance for gases is kept short
• a transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath
• long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight
• numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion pathway from one
• stomata that open and close in response to changes in light intensity
• many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen
• a network of xylem that brings water to the leaf cells and phloem that carries away the sugars produced by photosynthesis

Question 5

How does photosynthesis occur?

Answer 5

• photosynthesis is a complex metabolic pathway involving many intermediate reactions
• it is a process of energy transferral in which some of the energy in light id conserved in the form of chemical bonds

Question 6

What are the main stages of photosynthesis?

Answer 6

• capturing of light energy
• the light-dependent reaction
• the light-independent reaction

Question 7

What captures light energy?

Answer 7

-chloroplast pigments like chlorophyll capture light energy

Question 8

What is the light-dependent reaction?

Answer 8

• some of the light energy absorbed is conserved in chemical bonds
• during the process an electron flow is created by the effect of light on chlorophyll, causing water to split into protons, electrons and oxygen
• the products are reduced NADP, ATP and oxygen

Question 9

What is the light-independent reaction?

Answer 9

-protons are used to produce sugars and other organic molecules

Question 10

What is the structure and role of chloroplasts in photosynthesis?

Answer 10

• chloroplasts vary in shape and size but are technically disc shaped, 2-10 um long and 1 um in diameter
• they are surrounded by a double membrane with two distinct areas inside the grana and the stroma

Question 11

What is the grana?

Answer 11

• stacks of up to 100 disc-like structures called thylakoids where the light-dependant stage of photosynthesis takes place
• within the thylakoids is the photosynthetic pigment called chlorophyll
• some thylakoids have tubular extensions that join up with thylakoids in adjacent gran called inter-granal lamellae

Question 12

What is the Stroma?

Answer 12

• its a fluid killed matrix where the light-independent stage of photosynthesis
• within the Strom are a number of other structures such as starch grains

Question 13

What is the structure of a leaf?

Answer 13

• cuticle
• upper epidermis
• mesophyll (palisade)
• mesophyll (spongy)
• lower epidermis
• cuticle (guard cells and Stroma)