Human Reproduction

Enjoy and learn watching these videos about human reproduction!


How sperm gets in the egg

Menstruation animation

Ovulation

Menstrual Cycle

Male reproductive organ

Period of zygote

Prepositions: IN vs. AT vs. ON

Prepositions of Time: at, in, on

We use:

• at for a PRECISE TIME
• in for MONTHS, YEARS, CENTURIES and LONG PERIODS
• on for DAYS and DATES

at PRECISE TIME	in MONTHS, YEARS, CENTURIES and LONG PERIODS	on DAYS and DATES
at 3 o'clock	in May	on Sunday
at 10.30am	in summer	on Tuesdays
at noon	in the summer	on 6 March
at dinnertime	in 1990	on 25 Dec. 2010
at bedtime	in the 1990s	on Christmas Day
at sunrise	in the next century	on Independence Day
at sunset	in the Ice Age	on my birthday
at the moment	in the past/future	on New Year's Eve

Look at these examples:

• I have a meeting at 9am.
• The shop closes at midnight.
• Jane went home at lunchtime.
• In England, it often snows in December.
• Do you think we will go to Jupiter in the future?
• There should be a lot of progress in the next century.
• Do you work on Mondays?
• Her birthday is on 20 November.
• Where will you be on New Year's Day?

Notice the use of the preposition of time at in the following standard expressions:

Expression	Example
at night	The stars shine at night.
at the weekend*	I don't usually work at the weekend.
at Christmas*/Easter	I stay with my family at Christmas.
at the same time	We finished the test at the same time.
at present	He's not home at present. Try later.

*Note that in some varieties of English people say "on the weekend" and "on Christmas".

Notice the use of the prepositions of time in and on in these common expressions:

in	on
in the morning	on Tuesday morning
in the mornings	on Saturday mornings
in the afternoon(s)	on Sunday afternoon(s)
in the evening(s)	on Monday evening(s)

When we say last, next, every, this we do not also use at, in, on.

• I went to London last June. (not in last June)
• He's coming back next Tuesday. (not on next Tuesday)
• I go home every Easter. (not at every Easter)
• We'll call you this evening. (not in this evening)

Here you can practise prepositions of time

Prepositions of Place: at, in, on

In general, we use:

• at for a POINT
• in for an ENCLOSED SPACE
• on for a SURFACE

at POINT	in ENCLOSED SPACE	on SURFACE
at the corner	in the garden	on the wall
at the bus stop	in London	on the ceiling
at the door	in France	on the door
at the top of the page	in a box	on the cover
at the end of the road	in my pocket	on the floor
at the entrance	in my wallet	on the carpet
at the crossroads	in a building	on the menu
at the front desk	in a car	on a page

Look at these examples:

• Jane is waiting for you at the bus stop.
• The shop is at the end of the street.
• My plane stopped at Dubai and Hanoi and arrived in Bangkok two hours late.
• When will you arrive at the office?
• Do you work in an office?
• I have a meeting in New York.
• Do you live in Japan?
• Jupiter is in the Solar System.
• The author's name is on the cover of the book.
• There are no prices on this menu.
• You are standing on my foot.
• There was a "no smoking" sign on the wall.
• I live on the 7th floor at 21 Oxford Street in London.

Notice the use of the prepositions of place at, in and on in these standard expressions:

at	in	on
at home	in a car	on a bus
at work	in a taxi	on a train
at school	in a helicopter	on a plane
at university	in a boat	on a ship
at college	in a lift (elevator)	on a bicycle, on a motorbike
at the top	in the newspaper	on a horse, on an elephant
at the bottom	in the sky	on the radio, on television
at the side	in a row	on the left, on the right
at reception	in Oxford Street	on the way

Here you can practise prepositions of place