B3d Flashcards
What is the difference between simple organisms which are unicellular and more complex organisms which are multicellular?
Unicellular - single cells/ simple/ e.g. bacteria
Multicellular - multiple cells/ specialised organ system
What are the advantages of being multicellular?
Being multicellular means you can be bigger, meaning you can travel further, get your nutrients in a variety of ways and fewer things can eat you.
Being multicellular allows for cell differentiation. Instead of being just one cell that has to do everything, you can have different types of cells that do different jobs. Your cells can be specially adapted for their particular jobs.
Multicellular organisms can be more complex - they ca have specialised organs, different shapes and behaviour, and so can be adapted specifically to their particular environment.
Why does becoming multicellular require the development of specialised organ systems?
It needs…
- a system to communicate between different cells.
- a system to supply cells with the nutrients they need.
- a system that controls the exchange of substances with the environment.
What do most body cells contain?
Chromosomes in matching pairs.
What are new cells for growth produced by?
Mitosis.
What is mitosis needed for?
Replacement of worn out cells, repair to damaged tissue and asexual reproduction.
In mammals, what are body cells?
Diploid, two copies of each chromosome.
Prior to mitosis, how does DNA replication take place?
The DNA double helix first ‘unzips’ to form two single strands. New nucleotides then join on using complementary base pairing, making an exact copy of the DNA on the other strand. The result is two double-stranded molecules of DNA that are identical to the original molecule of DNA.
Why must DNA replication take place before cells divide?
So that each new cell still has the full amount of DNA. Also to give each chromosome two arms again.
What happens in mitosis?
The DNA coils into double-armed chromosomes. These arms are exact copies of each other. The chromosomes line up at the centre of the cell, and then divide as cell fibres pull them apart. The two arms of each chromosome go to opposite ends of one cell. Membranes form around each of these two different sets of chromosomes. The cytoplasm divides, and you get two new cells containing exactly the same genetic material.
What happens in sexual reproduction?
Gametes join in fertilisation.
What do gametes have?
Half the number of chromosomes of body cells.
How do you produce a unique individual through sexual reproduction?
Half the genes come from each parent.
Why are sperm cells produced in large numbers?
To increase the chance of fertilisation.
What are gametes produced by?
Meiosis.
