Prop roots Vs Stilt roots

1.Prop roots develop from the upper horizontal branches of the tree whereas stilt roots develop from the basal node of the plant stem.

2. Prop roots grow vertically whereas the stilt roots grow obliquely from the basal node.

3. Prop roots give support like a pillar whereas stilt roots work like ropes of a tent.

4. Young prop roots are hygroscopic whereas young stilt roots are not hygroscopic.

Prop roots are found in banyan whereas stilt roots are found in maize and sugarcane.

By: Ashwani Kumar,
biology teacher ,Phagwara

Difference between Tap root system and Adventitious root system

1.Tap root system arises from radicle of the embryo whereas the adventitious roots arise from any part of the plant body other than radical or its branches .They can arise from stem, leaves etc.

2.In tap root system there is single main root called tap root which bears branches in an acropetal manner .In adventitious roots there are number of equally strong fibrous roots present in clusters.

3.Tap root system is underground whereas adventitious roots may be underground or aerial.

4.In tap root system the primary root or tap root  persists throughout life of plant. In adventitious root system the primary root is short lived and is replaced by adventitious roots.

5.Tap root system may be deep feeder or surface feeder whereas adventitious root system is mostly surface feeder.

By: Ashwani Kumar,

Biology teacher,Phagwara

Difference between Respiratory roots and Assimilatory roots roots

1. Respiratory roots occur in plants growing in marshy areas whereas assimilatory roots occurs in plants growing in terrestrial and aquatic habitat and even in epiphytic plants.

2. Respiratory roots are non green
hence do not perform photosynthesis. Assimilatory roots are green and perform photosynthesis.

3. Respiratory roots are negatively geotropic . Assimilatory roots are diageotropic ,which means they tend to grow horizontal to the line of gravity .They may be plagio-geotropic which means they tend to grow at an angle oblique angle to the line of gravity.

4. Respiratory roots have covering of cork whereas assimilatory roots lack the covering of cork.

5.Respiratory roots have lenticels for gaseous exchange. Assimilatory roots lack lenticels. The gaseous exchange occurs through the general surface of roots.

6. Respiratory roots are modifications of tap root system whereas assimilatory roots are a type of adventitious roots.

By: Ashwani Kumar,
Biology teacher,Phagwara .

Differences between Gymnosperms and Angiosperms

1.The gymnosperms usually are not herbaceous, whereas, majority of angiosperms are herbaceous.

2. The gymnosperms are perennial whereas angiosperms may be annual biennial or perennial.

3. In gymnosperms the reproductive structures are cones which are unisexual, whereas, in angiosperms the reproductive structures are flowers which may be unisexual or bisexual.

4. In gymnosperms, during pollination the pollen grains fall on the micropyle , whereas in angiosperms they fall on the stigma.

5. In gymnosperms the pollination is  mainly occurs through anemophily whereas in angiosperms the pollination may occur through anemophily, entomophily ,hydrophily also .

6.Ovules are naked in gymnosperms ,whereas, they are protected in ovaries or carpels in angiosperms.

7. in gymnosperms the archegonia are present in female gametophyte, whereas, angiosperms lack archegonia.

8. In gymnosperms there is no double fertilization, only single fertilization occurs ,whereas, in angiosperms double fertilization occur.

9.Cleavage polyembryony is common in gymnosperms where is it is absent in angiosperms.

10. In gymnosperms zygote undergoes free nuclear division where is zygote of angiosperms does not divide by free nuclear division .

11.Vegetative reproduction is rare in gymnosperms, whereas, it is very common in angiosperms.

Dinoflagellates and Red Tides

Dinoflagellates are unicellular, eukaryotic organisms.most of the species are marine.some are found in freshwater.size ranges from 15 to 40microns.A species Noctiluca is larger ,can have size around 2mm.they have two flagella which help them to swim.their chromosomes are in highly condensed form.they have large quantity of DNA.although they are eukaryotes but they don't have histones.many dinoflagellates are photosynthetic.all are not photosynthetic.some dinoflagellates are symbiotic and live in marine invertebrates like sponges,corals,jellyfish etc some live within ciliates,foraminiferans and radiolarians.the non photosynthetic species are heterotrophic.they feed on other planktond or even on each other .noctiluca can even feed on fish eggs.several species of dinoflageyshow bioluminescence. dinoflagellates are second producers after diatoms in aquatic ecosystem. many genera of dinoflagellates cause red tide.these include Gonyaulax, Karenia ,Gymnodinium ,Dinophysis, Noctiluca, Chattonella,Amoebophyra.these contain photosynthetic pigments whose colour varies from brown to red. some red tides are bioluminescent.in addition to dinoflagellates red tides also contain diatoms.some red tides are harmful .some species of dinoflagellates causing red tides produce toxins which cause death of fishes. human can get affected by eating shell fish caught from water having red tide recently. shell fish feeds on dinoflagellates and eating toxic dinoflagellates in large amount during red tide cause accumulation of toxin inshell fish.eating such fish can cause serious health problems to man.

By: Ashwani,Biology Teacher,Phagwara.

Evolutionary role of Cyanobacteria

Cyanobacteria are a group of bacteria .they are photosynthetic .they are aquatic and are also found in moist soils. they have bluish green colouration. they are also called blue green algae because they arep photosynthetic and aquatic like algae.actually they are not algae but bacteria.algae are eukaryotes but cyanobacteria are prokaryotes.evolutionary they are very important group of organisms .their fossils have been traced back to 3.5bilion years ago . during evolutionary history of Earth they played important role by converting the reducing environment of Earth to oxidizing.they added oxygen to the earth environment by their photosynthetic activity.this paved the way for origin of aerobic organisms.they also played important role in origin of plants .according to endosymbiotic theory somewhere in proterozoic or Cambrian era a cyanobacteria entered a eukaryotic cell.here it found shelter and by photosynthetic activity provided food and oxygen to host cell also.gradualy this cyanobacteria got modified into chloroplast.
By : Ashwani,biology teacher,Phagwara.

Diatoms

Diatoms are a group of algae.they are found in oceans, freshwater bodies and even on moist soil.
ecologically they are very important.they produce 20% of oxygen produced on Earth.they are of different shapes, sizes and colours. they belong to division ochrophyta and class bacillariophyceae.
diatoms are solitary they can occur as solitary organisms or they may be colonial.when colonial,they may firm ribbon shaped,star shaped or zigzag colonies. the size of a diatom ranges from 2to 200 micrometers.their number increases very rapidly.if adequate sunlight and nutrients are available their number can become double in 24 hours. they mainly multiply by binary fission.
on the basis of shape diatoms have been classified into two categories. one is centric diatoms .they are radially symmetrical. other one is pennate diatom. they are bilaterally symmetrical. the life span of a diatom is about 6days. their cell wall forms a colourful case around them due to which diatoms are also called jewels of the sea. their cell wall form case or shell around individual cell. this case is called frustule. it is made up of silica, exactly hydrated silicon dioxide.in waterbodies they are passively carried away by water currents hence fall under phytoplankton.they cannot swim. however male gametes of centric diatoms can swim .most of the diatoms float passively on the surface of water.some are benthic found attached to the benthic substrates.diatoms are able to synthesize their food by photosynthesis.they are mostly restricted to the euphotic zone where sunlight can penetrate.their shell is unique having to two halves, upper larger one is called epitheca and lower one is called hypotheca.when a diatom divides each daughter cell receives one half of shell that is one valve which acts as epitheca.the daughter individuals develop new hypotheca. as hpotheca is smaller in size the daughter cell which receives hypotheca of parent cell, remember this hypotheca will act as epitheca in daughter cell and it will develop new hypotheca which will be smaller than epitheca.in this way this daughter cell will be smaller than parent cell even after full growth.after repeated binary fission the size of diatom cell will go on decreasing.it has been seen that after some binary fission's the diatoms undergo auxospore phase in which they increase in size and produce gametes by meiosis. dead diatoms sink to bottom of oceans and their shells  form diatomaceous earth.it is rich in silica and is s dynamite stabilizer.

1. By: Ashwani, Biology Teacher, Phagwara.