Question

1. Show a diagram of a plant membrane and show how the proton-ATPase sets up an electrochemical gradient. Then show specifically how the cation ammonium (NH₄⁺) would accumulate in a root hair cell against a concentration gradient using a uniport. Show also how the selenate anion (SeO₄^2- ) could be accumulated by a root cell using a symport, and how the Mn²⁺ ion would be exported from the cell using an antiport.     

2. Describe the characteristics of the two main types of mycorrhizae found in the plant kingdom, including morphology of the association, groups of plants and fungi, etc. Explain the nature of a typical mutualistic relationship that develops between the host plant and a fungus, and what substances are exchanged.

3.

Using diagrams and words, show how the Pressure Flow Model for Phloem Transport works. Be sure to show at the membrane level how phloem loading occurs at sugar sources (leaves) and how phloem unloading works at sinks.

Answer 1

1.

i) Cation ammonium (NH4+) accumulation: uniport

ii) The selenate anion (SeO4 2-) accumulation: symport

iii) Mn2+ ion export from the cell using an antiport:  

2.

i) Mycorrhizae 1: Ectomycorrhizae, they are the ones that associate with the plants externally and does not enter into the plant system. They are mainly Basidiomycota. E.g., Amanita spp., Boletus spp. They can be highly specific (for example Boletus elegans with larch) and non-specific (for example Amanita muscaria with 20 or more tree species).

ii) Mycorrhizae 2: Endomycorrhizae, they are the ones interconnected with the plant system and many times deeply rooted inside the plant root system.

Examples:

a) Arbuscular (AM) endomycorrhizas, which are the commonest mycorrhizas. The fungi are members of the Glomeromycota. E.g., Glomus mossae, associate with the grass species.

b) Ericoid endomycorrhizas are mycorrhizas of Erica (heather), Calluna (ling), and Vaccinium (bilberry).

A typical mutualistic relationship between a fungus and a host: One of the typical examples is of the vesicular-arbuscular mycorrhiza (VAM).

Another example is Ericoid Mycorrhiza. In their case the plant roots are covered with a sparse network of hyphae. The fungus helps in the digestion of polypeptides saprotrophically and after digestion, passes absorbed nitrogen to the plant host; Plant body help in the protection part and keep them safe with the plant nutrients like ammonia.

3. Pressure Flow Model for Phloem Transport: