Ten koszyk jest ciężki, bo mam w nim jogurt, banany i paprykę.

Because koszyk is a masculine singular noun in the nominative case, and the demonstrative ten must agree with it.

A quick comparison:

• ten = for masculine singular nouns
• ta = for feminine singular nouns
• to = for neuter singular nouns

So:

• ten koszyk = this basket
• ta torba = this bag
• to jabłko = this apple

Because adjectives in Polish have to agree with the noun they describe in gender, number, and case.

Here:

• koszyk is masculine singular nominative
• so the adjective also appears in the matching form: ciężki

That is why you get:

• ten koszyk jest ciężki but:
• ta torba jest ciężka
• to pudełko jest ciężkie

Bo means because.

It is a very common, natural word in everyday Polish. In this sentence, it explains the reason the basket is heavy.

You could also use:

• ponieważ = because
• gdyż = because / since

But bo is the most conversational and common choice here.

In Polish, a comma is normally used before conjunctions like bo, że, ponieważ, and others that introduce another clause.

So:

• Ten koszyk jest ciężki, bo mam w nim jogurt...

This is standard Polish punctuation.

Mam is the 1st person singular form of the verb mieć = to have.

So:

• mam = I have

In the sentence:

• mam w nim jogurt, banany i paprykę means:
• I have yogurt, bananas, and a pepper in it

Other forms of mieć:

• mam = I have
• masz = you have
• ma = he/she/it has
• mamy = we have

W nim means in it or in him, depending on what it refers to. Here it refers to koszyk, so it means in it.

Polish pronouns change form after prepositions. You cannot say w on. After w, the pronoun on/ono becomes nim.

So:

• on = he
• nim = him / it after a preposition

Examples:

• w nim = in it / in him
• na nim = on it / on him
• o nim = about him / about it

Here:

• w nim = in the basket

Because after mam (I have), the things you have are usually in the accusative case, and different noun types form the accusative differently.

Here is what happens:

• jogurt
  This is a masculine inanimate singular noun.
  For many masculine inanimate nouns, the accusative looks the same as the nominative.
  So:

  • nominative: jogurt
  • accusative: jogurt

• banany
  This is plural and non-masculine-personal.
  In that type, accusative plural is often the same as nominative plural.
  So:

  • nominative plural: banany
  • accusative plural: banany

• paprykę
  This is a feminine singular noun.
  Feminine nouns ending in -a usually change to -ę in the accusative singular.
  So:

  • nominative: papryka
  • accusative: paprykę

This is why the three objects do not all look the same.

Because papryka is a feminine singular noun, and after mam it is the direct object, so it must go into the accusative case.

For many feminine nouns ending in -a:

• nominative: -a
• accusative: -ę

So:

• papryka = subject form / dictionary form
• paprykę = object form

The same pattern appears in many other nouns:

• mam kawę from kawa
• widzę kobietę from kobieta
• jem sałatkę from sałatka

Because Polish case endings depend on the gender and type of noun.

Jogurt is masculine inanimate singular, and in that category the accusative is usually identical to the nominative.

So even though it is the object, it stays:

• jogurt

Compare:

• mam jogurt
• widzę stół
• kupuję chleb

But with a feminine noun:

• mam paprykę

And with a masculine animate noun:

• mam kota from kot

So the object case is still there, but sometimes it is not visible as a different ending.

It can mean either, depending on context.

• papryka can mean pepper / bell pepper as a vegetable
• it can also mean paprika as a spice

In this sentence, because it is in a basket with jogurt and banany, the natural meaning is the vegetable.

If needed, Polish speakers can make it more specific:

• papryka czerwona = red pepper
• papryka w proszku = paprika powder

Historically, koszyk is related to kosz and has a diminutive feel, something like small basket. But in modern Polish, koszyk is the normal everyday word for many kinds of baskets, especially things like a shopping basket.

So in practice, learners can usually just understand koszyk as:

• basket

A few related words:

• kosz = basket / bin / hamper, depending on context
• koszyk = basket, often the more common everyday word for a portable basket

Not completely. Polish word order is more flexible than English because case endings show grammatical relationships.

The neutral order here is:

• Ten koszyk jest ciężki, bo mam w nim jogurt, banany i paprykę.

But other orders are possible for emphasis, for example:

• Ten koszyk jest ciężki, bo w nim mam jogurt, banany i paprykę.
• Bo mam w nim jogurt, banany i paprykę, ten koszyk jest ciężki.

Those alternatives are grammatically possible, but the original sentence sounds the most natural and straightforward in normal speech.

Normally, no. In this sentence, jest is the present-tense form of być = to be, and it is needed in standard Polish.

So:

• Ten koszyk jest ciężki = correct

If you say:

• Ten koszyk ciężki

that sounds incomplete in standard Polish, though something like that might appear in very informal speech, notes, headlines, or stylized language.

Because w nim belongs closely with mam and tells you where the items are.

So:

• mam w nim jogurt, banany i paprykę literally works like:
• I have in it yogurt, bananas, and a pepper

This is a very natural placement in Polish. It makes the location clear before naming the items.

You could move it for emphasis, but the original order is neutral and idiomatic.