Auxins

Auxins:

  • Term ‘auxein’ means to grow.
  • Weak organic acid
  • Found in the root & shoot tip.
  • Shows polar movements: i.e., shoot tip downwards & root tip upwards.
  • Charles Darwin & his son Francis Darwin: 1st reported the presence of auxin in the coleoptile of canary grass (Phalaris). They showed that the coleoptile started growing towards unilateral illumination (phototropism), while the decapitated coleoptile did not.

  •  F W Went: Performed the Agar block experiment in Avena coleoptile (oat). He decapitated the tip of Avena coleoptile and kept it on an agar block, he later replaced the tip with agar block, the coleoptile started growing towards the light.
  • Went named it as ‘Auxin’.

 

  • Kogl & Haagen-smith: Isolated it from human urine.
  • Natural auxins:

    Indole 3-acetic acid (IAA) & Indole butyric acid (IBA).

  • Synthetic auxins:

    2,4-dichlorophenoxy acetic acid (2,4-D), Naphthalene acetic acid (NAA) & IBA.

Continue reading

Clotting factors – Mnemonic

Clotting factors: 

  • The clotting factors are a group of chemicals in the blood which is responsible for the formation of blood clot.
  • Clotting factors are usually inactive but once there is an injury to the wall of the blood vessel, they get activated.
  • The function of clotting factors is to trigger the formation of a blood clot and stabilize it for as long as necessary.
  • Clotting factors are therefore known as procoagulants.

MNEMONIC for Clotting Factors:

Freshers Party Tonight! Come Let’s Sing & Also Call Seniors Please Have Fun.

Factor I – Fibrinogen; common pathway; converted to fibrin.

Factor II – Prothrombin; common pathway; converted to thrombin that converts fibrinogen to fibrin.

Factor III – Tissue factor (TF) or thromboplastin; extrinsic pathway.

Factor IV – Calcium ions (Ca2+); always present, needed for coagulation.

Continue reading

Digestive Enzymes

DIGESTIVE ENZYMES:

Digestion of carbohydrates:

In oral cavity:

By Saliva:
  • Amylase (ptyalin) converts starch & glycogen → Maltose.

In the small intestine:

By Pancreatic juices:
  • α – Amylase converts starch → Maltose.
By Intestinal juices:
  • Maltase converts maltose →glucose.
  • Sucrase converts sucrose → glucose & fructose.
  • Lactase converts lactose → glucose & galactose.

Digestion of proteins:

In stomach:

By Gastric juices:
  • HCl provides acidic pH.
  • Pepsinogen (proenzyme) converted by HCl into Pepsin.

Pepsin converts protein into peptones & proteoses.

  • Prorenin (proenzyme) converted by HCl into Renin.

Renin converts Casein (milk protein) into peptides.

Continue reading

Gymnosperms

Gymnosperms

Belong to the group Phanerogams i.e., seed bearing plants. They have naked seeds (not enclosed within a fruit). They are mainly xerophytes.

  • Have diplontic life cycle.
  • Plant body is the sporophyte & the gametophytic generation is very much reduced.
  • Sporophyte is well differentiated into root, stem & leaves.
  • Roots: Tap root system.
  • Stem: Thick, woody with scars of fallen leaves.
  • Leaves are 2 types: foliage leaves & scale leaves.
  • They are either monoecious or dioecious.
  • Secondary growth occurs.
  • They are heterosporous and bear male & female cones.
MALE REPRODUCTIVE PART:
  • Male cones are smaller in size & short lived.

They consist of spirally arranged microsporophylls.

Microsporophyll bear microsporangia inside which the microspores/pollens are produced after meiosis.

Pollen/microspore starts dividing in the microsporangium.

They produce 1-2 prothallial cells, a generative cell & a tube cell.

Further development occurs after pollination.

The generative cell divides to form body cell & stalk cell. The body cell then produces 2 male gametes. Tube cell forms the pollen tube carrying the male gametes.

 

 

Continue reading

Vascular tissue system

Vascular tissue system

  • Constitute the vascular bundles.
  • Procambial strands of plerome of apical meristem forms the vascular tissue.
  • It consists of xylem & phloem.

Xylem(wood) is made of tracheids, vessels, xylem parenchyma & xylem fibres.

Phoem(bast) is made of sieve elements, companion cells, phloem parenchyma & phloem fibres.

  • Early formed xylem & phloem are referred as protoxylem & protophloem.
  • Later formed are referred as metaxylem & metaphloem.

 

VASCULAR BUNDLES:

  • Are of 2 types:
  1. RADIAL:

Xylem & phloem form separate bundles present on different radii.

Xylem is exarch i.e., protoxylem towards periphery & metaxylem towards the center.

Found in roots.

Continue reading