Physics Homework need help

A vacuum flask is designed to reduce the rate of energy transfer by hearing processes. Describe how the design of a vacuum keeps the liquid inside hot.

Energy is transferred by the process of convectio from the hot water at the bottom of the tank to the cooler water at the top. Explain how.

Please help me with question 4a and 5a as I am completely stuck on them. I have put the web address for the paper. Would really appreciate any help and I need to have finished this by next Friday (5th September). I have been trying the questions for about 2 weeks now and I just can't seem to do them. Have looked for the answers everywhere and can't find them.

http://filestore.aqa.org.uk/subjects/AQA-PH1HP-QP-JUN13.PDF

Welcome to TSR physics.
Here are a few tips to getting replies on here.
1. Please post the actual question, and not a link to the paper on another website.
2. Say what you need help on and what you don't understand.

These questions are about convection conduction and radiation. Heat transfer.

For the vacuum flask any Google search should find you the required information. Try this for a start.
http://www.bbc.co.uk/learningzone/clips/heat-transfers-and-the-vacuum-flask/10670.html

For the immersion heater question take a look at this.
http://www.ehow.co.uk/about_5170548_immersion-heater_.html

You need to attempt the questions yourself first. We can then help you with your answers.

Thanks and I did