Autotrophic Nutrition Flashcards
What is Autotrophic nutrition?
This is the process by which organisms take in inorganic carbon and energy, to form complex organic compounds.
Explain the types of Autotrophs
(1) Phototrophs - organisms which synthesize organic compounds using light energy. e.g. all green plants, algae, cyanobacteria, blue-green bacteria, green sulphur bacteria, purple sulphur bacteria, colourless sulphur bacteria.
(2) Chemotrophs - organisms which synthesize organic compounds using energy extracted from oxidation of inorganic chemicals by the process called chemosynthesis e.g. Nitrosomonas and Nitrobacter
What is Chemosynthesis?
This is a chemical process in which inorganic chemicals are oxidized to provide energy to living organisms for the synthesis of organic compounds.
The chemosynthetic bacteria utilize the energy from the chemical oxidation of inorganic chemicals to synthesize organic compounds, some of which are subsequently oxidized in respiration to yield energy for metabolism.
Define photosynthesis
It is the formation of complex organic substances inside the cell containing chlorophyll from carbon dioxide and water using sunlight energy.
What is the importance of photosynthesis?
- It is the means by which the sun’s energy is captured by plants for use by all organisms.
- It provides a source of complex organic molecules for heterotrophic organisms.
- It releases oxygen for use by aerobic organisms.
- It reduces on gaseous carbon dioxide, which would accumulate in the atmosphere to cause green house effect.
What are the adaptations of leaves to obtaining sunlight?
- Phototropism causes shoots to grow towards light in order to obtain energy.
2.Etiolation causes rapid elongation of shaded shoots to enable access to light. - The mosaic leaf arrangement minimizes leaf overlap and reduces leaves shading each other.
- Leaf large surface area enables capturing maximum sunlight.
- Thinness of leaves enables maximum light penetration.
- The transparence of leaf cuticle and epidermis allow light penetration into the photosynthetic mesophyll.
- The palisade mesophyll cells are densely packed with chloroplasts to trap much light.
- Cyclosis (movement of chloroplasts within the mesophyll cells) allows repositioning in the direction of light.
- The chloroplasts hold chlorophyll in an ordered way on the sides of the grana to present maximum chlorophyll to the light and also bring it close to other pigments / substances necessary for functioning.
- Multiple cell layers in the palisade mesophyll of sun plants increases photosynthetic efficiency.
What are the adaptations of leaves for gas entry and exit?
- Numerous stomata are present in the epidermis of leaves to enable entry and exit of gases.
- The guard cells bordering stomata pores can be opened and closed to regulate the uptake of carbon dioxide and the loss of water.
- Spongy mesophyll possesses many airspaces to enable faster and uninterrupted diffusion of gases between the atmosphere and the palisade mesophyll which wouldn’t happen if the gases were to diffuse through the cells themselves, a process which would be much slower.
What are the adaptations of leaves for liquid entry and exit?
- A large central midrib containing a large vascular bundle comprising xylem and phloem tissue is possessed by most dicotyledonous leaves for the entry and transport of water and mineral salts, and the phloem for carrying away sugar solution, usually in the form of sucrose.
- A network of small veins is found throughout the leaf to ensure that every cell is close to xylem vessel or phloem sieve tube for constant supply of water for photosynthesis and a means of removing the sugars they produce.
What are the adaptations of chloroplasts to their functions?
- Outer membrane is semi- permeable to regulate entry and exit of substances for maintaining internal chloroplast environment.
- Abundant light trapping pigments for photosynthesis
- Abundant enzymes catalyse photosynthetic reactions in the stroma.
- Extensive network of thylakoid membranes increase surface area for photosynthesis.
- Narrow intermembrane space enables H+ ion concentration gradient to be rapidly established for chemiosmosis to occur
- Inner membrane contains molecules for electron transport pathway
- DNA presence codes for protein synthesis, including enzymes.
- Many ribosomes for protein synthesis to reduce on importing proteins from cytoplasm.
- Outer membrane is permeable to gases like carbon dioxide which is a raw material for photosynthesis.
What are the two types of photosynthetic pigments?
- Chlorophyll (alpha and beta)
- Cartenoids (accessory pigments; hand over energy absorbed to chlorophyll a)
Function of both is to absorb light
- Cartenoids also protect chlorophyll from photo damage
What is the difference between incandescence and luminescence?
Incandescence is the emission of light from hot matter e.g. the sun. (The hotter the material, the shorter the wavelengths of emitted light, the more the energy)
While
Luminescence is the emission of light when ‘excited’ electrons fall to a lower energy, emitting a photon e.g. the light- emitting diode bulbs in school labs, fluorescent lights, light from leaf extracts, etc.
What are the three ways in which light interacts with a leaf?
- Reflection (Reflectance): light can simply rebound off the leaf surface and hence never utilized in leaf photosynthesis.
- Transmission (Transmittance) through the leaf, exiting from the underside.
- Transmission depends on the thickness of the leaf; thin leaves transmit more light than thick leaves
- Absorbance by the leaf, in which case the light might be used in photosynthesis.
- Of the absorbed visible radiation, 70%, is used in photosynthesis while 30% is transmitted through the leaf.
- Blue and red are the most absorbed wavelengths, and green and far infrared wavelengths pass through.
True or false
The amount of sunlight decreases as light penetrates down the vegetation layers
True
This is because the amount of leaf area increases.
What does magnesium deficiency in plants cause?
Chlorosis
What issues are faced by plants in different light intensities?
- In low light, plants need to maximise light absorption for photosynthesis to exceed respiration if they are to survive.
- In high light environment, plants maximise their capacity for utilising abundant light energy, while at the same time dealing with excess sunlight which can bleach chlorophyll.
What are the adaptations of shade plants to photosynthesis in their habitat?
- Abundant chlorophyll b (low chlorophyll a to chlorophyll b ratio) which gives leaves dark green colour to increase light absorption in the dark;
- Palisade/ spongy mesophyll ratio low (few palisade, more spongy) to allow maximum light penetration;
- Mesophyll cell surface / leaf area ratio low to maximise light trapping;
- Leaf orientation horizontal to maximise light trapping;
- Reddish leaf undersides to enhance reflectance back up through the photosynthetic tissue; giving the plant a second chance to utilize the light.
- Stomatal density low to avoid over cooling;
- Thin leaves to maximise light penetration;
- Stomatal size large to allow loss of excess water;
- Elongated internodes for increased access to light;
- Chloroplast size large to increase the surface area for storage of photosynthetic pigments.
What are the adaptations of sun plants to photosynthesis in their habitat?
- Abundant chlorophyll a (high chlorophyll a to chlorophyll b ratio) to increase light absorption;
- Palisade/ spongy mesophyll ratio high to minimise light penetration;
- Mesophyll cell surface / leaf area ratio high to minimise excessive light and transpiration;
- Leaf orientation erect to minimise light trapping;
- Stomatal density high to avoid over heating;
- Much carotenoids to prevent damage to chlorophyll from very bright light.
- Thick leaves to minimise light penetration
- Stomatal size small to minimise water loss;
- Much chlorophyll
Why is the ratio of chlorophyll a : chlorophyll b is bigger in sun leaves than shade leaves?
Sun leaves contain more chlorophyll a than shade leaves because chlorophyll a is more effective at absorbing the light wavelengths available to sun leaves e.g. about 450 nm.
Shade leaves contain more chlorophyll b than sun leaves because in shade plants chlorophyll b improves light- capturing capability of the chloroplast.
Sun leaves contain more carotenoids than shade leaves because carotenoids are accessory pigments that shield chlorophylls from destruction by excessive sunlight.
Why is it that few species of plants can survive under shady habitats?
- Less direct light reaches ground via gaps in the canopy hence minimum energy is available for effective photosynthesis.
- Of the light that passes through leaves, only a small range of wavelengths reaches the ground, which is not effective for photosynthesis.
- Therefore, under shady habitats little light energy is available for chlorophyll to absorb and hence photosynthesise is insufficient for growth.
Describe the chlorophyll molecule structure
- Chlorophyll molecule has a tadpole-like structure
- A hydrophilic head
- A hydrophobic tail made up of long chain alcohol.
- The flattened head is made up of four nitrogen rings
- The skeleton of each pyrrole ring is made up of 5 atoms - four carbon and one nitrogen.
- The nitrogen lies towards the centre.
- A magnesium atom is held in the centre of porphyrin head
What is the absorption spectrum of photosynthetic pigments?
It is a graph of the relative absorption of different wavelength of light by a pigments like chlorophyll.
What is the action spectrum of photosynthesis?
A graph of the effectiveness of different wavelengths of light in stimulating the photosynthetic process.
It represents the actual rate of photosynthesis in living cells.
What are the two stages of photosynthesis?
- Light dependent stage
- Light independent stage (Calvin’s cycle)
Where does the light independent stage of photosynthesis take place?
Thylakoids in the chloroplasts
What are the products formed after the light independent stage of photosynthesis?
- ATP
- NADPH
What is the main function of the light independent phase of photosynthesis?
- Photophosphorylation i.e. addition of an inorganic phosphate to Adenosine diphosphate (ADP) to form Adenosine triphosphate (ATP) using light energy.
- Formation of NADPH+ which is the reduced form of Nicotinamide adenine dinucleotide phosphate.
