Posted on

Humus – What is it? | NCERT Science Class VII | Chapter 17 | (Gujarati Explanation for Eng Medium)

Humus is formed by decomposers such as bacteria, fungi, beetle, ants etc which falls under the saprotrophs. These decomposers decomposes or degrades the dead matter fallen on the forest floor such as leaves, plant parts, fruits, dead animal remails, fecal matter etc and converts it into dark colored substance. This dark color substance is called Humus.

Humus forms the top layer of the soil. It is very rich in nutrients. Eventually it gets absorbed by roots of plants from soil and therefore, it increases the soil fertility.

Remember: Based on how animals, plants and organisms obtain their food, they are divided into different categories such as autotrophs, heterotrophs and saprotrophs.

Saprotrophs : (sapro = dead); feeds on dead or decaying matter; e.g: yeast, bacteria, fungi, mushroom, beetles, ants, insects

This video explains what is humus from the chapter 17 of NCERT science class VIII in Gujarati for English medium.

Forests: Our Lifeline | Part 1 | Forests, Shrubs, Herbs, Creepers & Climbers

NCERT Science Class VII | Chapter 17 | Forests: Our Lifeline (Gujarati Explanation for Eng Medium) 2

Herbivores, Carnivores & Omnivores | Autotrophs, Heterotrophs & Saprotrophs | NCERT Science Class VII

You can find this chapter online on NCERT e-book here : NCERT Science Class VII Chapter 17.

Posted on

MHC I vs MHC II – What is the Difference?

MHC I vs MHC II – What is the Difference?

(MHC I vs MHC II)  Major Histocompatibility Complexes plays crucial role in activating Cell Mediated Immunity in our body. Tc cells and Th cells cannot recognise the peptide alone, they have to be presented peptides on MHC molecules.

MHC molecules present in humans are called HLA – Human Leucocyte Antigen. MHC molecules binds to peptide fragments derived from antigen degradation and display them on the cell surface for recognition by the appropriate T cells. It is also responsible for graft rejection.

MHC class I is present in all nucleated cells. RBCs does not have a nucleus and therefore does not contain MHC class I. It presents the peptide to Tc cells and thus they are involved in clearance of endogenous Ag.

MHC class II is present in Antigen Presenting Cells (APC) such as B cells, dendritic cells, macrophages. It presents the peptide to Th cells and thus they are involved in clearance of exogenous Ag.


Antigen Processing and Presentation | Part I | The Cytosolic Pathway

Antigen Processing and Presentation | Part II | The Endocytic Pathway

Reference book to follow for this topic: Kuby Immunology