Thursday, 28 February 2013

homework 28th feb


1.Make a glossary of new terminology from this lesson.
2.Produce model answers for the exam questions on the blog.
3.Watch wonders of life
4.Read notes on the blog and elaborate with your own notes.

Thursday, 21 February 2013

images for gas exchange in plants






DNA trip

I am writing to tell you about the exciting opportunity we have been given to take a group of students to the Oxford University Museum of Natural History for a DNA workshop. This event takes place on Friday 1st March 2013, 9.30-3.00 pm.  

Students will use PCR to investigate human evolution. It will involve them analysing and comparing their version of a bitter taste receptor gene to their ability to taste. Students will learn about molecular biology techniques by using research-quality equipment. The workshop will be relevant for all Year 12 Biologists as it complements several areas of the course.

We will meet outside Oxford University Museum of Natural History at 9.15am on the Friday; students will have to make their own way to and from the Museum for this visit and will be registered on site. Students will need to bring a packed lunch and a drink as there are no lunch facilities at the museum.

Homework-21st feb


1.Watch the ‘wonders of life’ episode- size matters
(great information about how the size of organisms is linked to their surface area to volume ratio)
2. Revise structure of plant cells and leaves for next Thursday
3. Revise DNA structure for workshop on Friday! Hand in your slip if you haven't already so you have a reserve place.

Tuesday, 19 February 2013

Homework!


1.Watch the ‘wonders of life’ episode- size matters
(great information about how the size of organisms is linked to their surface area to volume ratio)
2. Revise structure of plant cells and leaves for next Thursday
3. Revise DNA structure for workshop on Friday! Hand in your slip if you haven't already so you have a reserve place.

Have yourself prepared for the 1st March

Problem for fish!


Gas exchange is more difficult for fish than for mammals because the concentration of dissolved oxygen in water is less than 1%, compared to 20% in air. 

structure of fish gills

countercurrent & parallel current principle


Summary of gas exchange in fish gills


1.Fish have developed specialised gas-exchange organs called gills, which are composed of thousands of filaments.
2.The filaments in turn are covered in feathery lamellae which are only a few cells thick and contain blood capillaries.
3.This structure gives a large surface area and a short distance for gas exchange.
4.Water flows over the filaments and lamellae, and oxygen can diffuse down a concentration gradient the short distance between water and blood, whilst CO2 diffuses in the opposite direction, also down its concentration gradient.
5.Each gill is covered by a muscular flap (the operculum) on the side of a fish's head.
6.The gills are so thin that they cannot support themselves without water, so if a fish is taken out of water after a while the gills will collapse, the SA/Vol ratio falls, and the fish suffocates.

Wednesday, 6 February 2013

Tuesday, 5 February 2013

Wonders of life expanding universe

http://www.bbc.co.uk/iplayer/episode/b01qm913/Wonders_of_Life_Expanding_Universe/

Remember to bring in your reply slip!

Bring in the slip asap and I can put you on the list to go. If I am not here put it under the door or come find me in the science staff room.

Thanks
Ms Timms :)

SA/vol ratio summary


As organisms get bigger their volume increases by the cube of their size, whilst their surface area increases by the square of their length
= so volume increases much faster than surface area.

As the size of the organism increases the surface area to volume ratio gets smaller


SA/vol ratio practice question

 
Explain the link between the size of an organism and the way in which its cells are supplied with oxygen.
(6)


mark scheme:
Note: Accept converse argument throughout
Small organisms have large surface/volume ratio;

as, for example, most
protoctista/single-celled
organisms/platyhelminths/cnidaria; diffusion/exchange over body surface/skin;

(the need for) specialised respiratory/gas-exchange surfaces in larger
animals
;

diffusion is a slow
process;
cells of larger organisms are a long way from gas exchange surface;

must be supplied by transport system/circulatory system/blood; 
max 6

Surface area to volume ratio images